Cabbage Integrated Pest Management : An Ecological Guide.

Why this guide?About this guideThis ecological guide is developed by the FAO Inter-Country Programme for IPM in vegetables in Southand Southeast Asia. It is an updated version of the Cabbage IPM Ecological Guide dated June 1996.The objective of this ecological guide is to provide general technical background information on cabbageproduction, supplemented with field experiences from the National IPM programmes connected to FAO’sVegetable ICP, and from related organizations active in farmer participatory IPM.Reference is made to exercise protocols developed by Dr. J. Vos of CABI Bioscience (formerly IIBC/CABInternational) for FAO. The exercises are described in “Vegetable IPM Exercise book”, 1998 whichcontains examples of practical training exercises that complement the technical background informationfrom this guide.Who will use this guide?National IPM programmes, IPM trainers, and others interested in IPM training and farmer participatoryresearch.How to use this guideThe ecological guides are technical reference manuals. They give background information and refer toexercises/studies that can be done in the field during training of trainers (TOT), farmers field schools(FFS) and action research to better understand a topic.The information in the guides is not specific for one country. Rather, this guide is an inspirational guidethat provides a wealth of technical information and gives ideas of IPM practices from several countries,mainly from the Asian Region, to inspire IPM people world-wide to conduct discovery-based IPM trainingand to set up experiments to see if such practices would work in their countries and continents ofassignment.IPM cannot be mastered through books or guides: the field remains the main learning base. This is whythe link with the exercise manual mentioned above is important.National programmes can use the guides to prepare training materials like hand-outs specific for atraining activity. The ecological guides can be used as ‘working copies’ or as basis for preparation of IPMcurricula and materials for farmer-trainers.The FAO Vegetable ICP hopes that this guide may be aninspirational toolfor discovery-based IPM training and farmer participatory research.1 Cabbage Ecological Guide - 2000

Introduction1INTRODUCTION1.1 Integrated Pest Management : beyond bugs…Integrated pest management, IPM, is still strongly associated with pests, however, it is much more thanjust pest control. IPM is not about eliminating all pests, in fact, low level populations of some pests areneeded to keep natural enemies in the field. The aim of IPM is to reduce pest populations to avoiddamage levels that cause yield loss. The entry point of an IPM programme may often be focused onreduction of pesticide use. However, the basis of good crop management decisions is a better understandingof the crop ecosystem, including that of the pests, their natural enemies, and the surroundingenvironment. Monitoring of the crop is the first step into understanding ecosystems.Experiences over several years with vegetable IPM show that good crop management practices maylead to reduction of inputs (including pesticides), without reduction in yield. In fact, yields often increasein IPM fields.In Vietnam for example, the average pesticide use in 150 FFSs in the period winter 1996 to summer1999, was only 40% of that of untrained farmers. Yields of cabbage in the same period were slightlyhigher (about 6%) in the IPM field as compared to the Farmer Practice control.IPM strategies are different for each crop, for a country, for a region, even for one location, depending onlocal varieties used and local agronomic practices. IPM can never be delivered in a “package”, it needs tobe developed, adapted, tailor-made to fit local requirements. Yet, experiences from one area, or fromother countries may be helpful to set up field studies for testing the components that may lead totolerable pest populations and a high yield of good quality produce. Some of these experiences andpractices are summarized in this guide.Cabbage Ecological Guide - 20002

Introduction1.4 Cabbage: a bit of historyThe Latin name for cabbage isBrassica oleracea var. capitata,member of the family Crucifers.Similar to many other vegetables,cabbage is not indigenous to Asia.It originates in Western Europe, withtemperate climates. A kale-like ancestorwas grown in gardens as farback as the time of the Roman Empire.In Europe, cabbage gardenswere very important food sourcesduring the Middle Ages.It is not exactly known how cabbageand other vegetables came to Asia.However, some literature references mention European vegetables in Asia. For example, Sir WilliamBaker, Governor of Ceylon for 7 years in the middle of the last century, mentioned that potatoes and otherEuropean vegetables were already cultivated around the Hill Station Nuwara Eliya specializing in thecultivation of European vegetables. These included potatoes, cabbage and leeks. Until the end of WorldWar II European vegetables were mainly grown to supply the European communities and for shipsstopping in the harbour of Colombo and Trincomalee.A similar development could be seen in the Nilgiri Hills in India and the Cameron Highlands in Malaysia.(Baker, 1966; Senewiratne and Appadurai, 1966; Macmillan, 1936)Most cole crops are in the species Brassica oleracea. Differences in morphology between cole crops areundoubtedly the result of early selection by farmers for various edible parts. This selection is easybecause all cole crops can be crossed and many are self-incompatible (i.e., flowers cannot be fertilizedby pollen from the same plant). These characteristics have made it easy to select for new types of colecrops. Self-incompatibility also makes hybrid seed production economical.Cabbage Ecological Guide - 20004

Cabbage Crop Development2CABBAGE CROP DEVELOPMENTSUMMARYThis chapter describes general growth stages for cabbage. Accurate growth stagedescriptions are very useful in pest management since plant susceptibility to pestsvaries with the growth stage. Some growth stages can tolerate damage by certaininsect pests or diseases whereas in other stages crop damage may result in yieldloss. Trials to study the ability of the cabbage plant to compensate for pest injuryat particular growth stages is an important element of IPM field studies.A table in this chapter indicates the susceptibility of growth stages to injury fromvarious insect pests and diseases. It can be used to develop, with farmers, amore appropriate growth stages description (or cropping calendar) for your area,based on locally used varieties and terminology.5 Cabbage Ecological Guide - 2000

Cabbage Crop DevelopmentPresently there is no standard terminology for describing cabbage growth stages like there is for rice.Although terms such as “head formation” and “cupping” do exist, it can be confusing because thisterminology is often regional and can vary among farmers and others involved in agriculture. Accuratecabbage growth stage descriptions are particularly useful in pest management since plant susceptibilityto cabbage pests varies with the growth stage.As an example, this chapter describes cabbage growth stages as they are used in the U.S.A. It alsolists the susceptibility of these growth stages to injury from various insect pests and diseases. Thegrowth stages below can used to develop, with farmers, a more appropriate growth stage description orcropping calendar for a specific area, based on locally used classification.(modified from Andaloro, J.T. et al, 1983)2.1 Cabbage growth stagesStage 1 : Cotyledons (seed leaves).No true leaves present.Stage 2 : SeedlingUp to 5 true leaves.Stage 3: 6 to 8 true leavesready for transplantingStage 4: 9 to 12 true leaves.Base of stem still visible from above.Stage 5: Precupping. Approximately 13 to 19leaves. By the end of this stage, the base of thestem and the bases of all leaves are concealedwhen the plant is viewed from above. Theinnermost heart leaves are growing in an uprightfashion and are visible without moving any of thesurrounding leaves.Cabbage Ecological Guide - 20006

Cabbage Crop DevelopmentStage 6: Cupping. Approximately 20 to 26leaves. The innermost heart leaves, which arestill growing in an upright fashion, are concealedby the larger, older leaves surrounding them. Allvisible leaves will later become the frame leaves(leaves not touching the mature head) of themature plant.Stage 7: Early head formation. Head diameterwill be approximately 10 cm. The inner heartleaves, now quickly developing as a ball-likestructure of overlapping leaves, are concealed bythe surrounding larger leaves. These leaves donot press tightly against the developing head andwill later unfold to become frame leaves.Stage 8: Head fill. Head diameter will beapproximately 10 - 20 cm. A firm roundhead is visible within the wrapper leaves(the 4 outer loose leaves that touch themature head). The head has not yet fullydeveloped and thus, is not ofharvestable size.Stage 9: Mature. Head diameter will beapproximately 15 - 30 cm. No new visible leafproduction will occur after the head hasattained maximum hardness and size. Thehead is ready for harvest and may split if notharvested in time.7 Cabbage Ecological Guide - 2000

Cabbage Crop Development2.2 Susceptibility of growth stages to cabbage pestsWhether various pest and disease species that attack cabbage plants will cause yield loss dependspartly on the growth stage of the plant. Injury to the older leaves at a late stage in crop development forexample, will not influence the final yield. Spraying a fungicide to control a slight Alternaria leafspotinfection occurring at the older leaves, is simply a waste of money.For fresh market cabbages for example, the quality could be reduced if even slight injury occurs on thewrapper leaves or the head. In earlier stages, stages 1 to 6 however, the wrapper leaves are not yetpresent and injury need only be prevented if a loss in head weight (yield) is expected. The cabbage plantcan compensate for a lot of injury by producing more leaves.In the TOT and FFS, studies on defoliation and removal of the growing point can be conducted to obtaininformation about compensation ability of the cabbage plant. An example is given in the box below.Compensation study result from Ban Nongkeo, Vientiane, Lao PDRDuring a field study by farmers of the village of Ban Nongkeo, farmers defoliatedcabbage plants for 25% and 50% at both 14 and 28 days after transplanting(DAT) and looked at resulting yields compared to an undefoliated control.Defoliation simulates the effect of leaf damage due to leaf-eating insects like diamondbackmoth.L A O SFarmers found that all 4 defoliation treatments had no effect on yield compared to the control,in fact, yields were the same or slightly higher in the treatments. Farmers concluded thatlimited defoliation in the first month after transplanting did not affect yield.(from: FFS on IPM in tomato and cabbage, Lao PDR, Nov 98 – Mar99).Some pests are present throughout the season and can affect cabbage at any growth stage. They willonly affect the quality or yield at susceptible growth stages. Damage, and impact of damage on yield, willalso depend on the cabbage variety grown, and other elements of the ecosystem like natural enemies,weather conditions, fertilizer, water availability and so on.Always analyse all components of the agro-ecosystem andtheir interactions when making crop management decisions!The following table (2.2) shows when potential injury from common cabbage pests and diseases mayoccur at specific growth stages. Please note that these are general values. There may be considerabledifference in each region!Cabbage Ecological Guide - 20008

Cabbage Crop DevelopmentTable 2.2 : Susceptibility of growth stages to cabbage pestspest/diseaseDamping - off( Pythium sp.)growth stagecotyledonsseed -ling6 - 8trueleaves9 - 12trueleavesprecuppingcup -pingearlyheadforma -tionheadfillmatureFlea beetles ( Phyllotretasp.)Cutworm( Agrotis sp. )Black leg( Phoma lingam )Black rot ( Xanthomonassp.)Diamondback moth( Plutella xylostella )Webworm( Hellula sp.)Cabbage worm( Pieris sp.)Stemborer( Melanagromyza sp.)Downy mildew( Peronospora sp.)Clubroot( Plasmodiophora sp.)Aphids( Brevicoryne sp.)Cabbage looper( Trichoplusia ni )Armyworm ( Spodopterasp.)Heart caterpillar( Crocidolomia sp. )leaf spot( Alternaria sp.)Soft rot( Erwinia carotovora )Whitefly( Bemisia sp.)Bottom rot( Rhizoctonia sp.)dark gray area : main pe st occurrencelight gray area : pest occurs to lesser extentRelated exercises from CABI Bioscience/FAO manual:2.1. Crop stages and plant parts2.2. Monitor crop stages2.3. Crop needs per crop stage2.4. Plant roots and vessels2.5. How to grow a healthy crop4-A.3. Plant compensation studies9 Cabbage Ecological Guide - 2000

Major Agronomic Practices3MAJOR AGRONOMIC PRACTICESSUMMARYA few general rules for good agronomic practices are:l Select a variety suitable for your climate/environmental conditions, possiblywith resistance against pest(s) or disease(s).l Use clean seed, and/or clean planting material.l Add lots of compost (or other decomposed organic material) to the soil everycropping season, both to nursery sites and to the main field.l When a lot of organic material is used, use low amounts of chemical fertilizers.l Practice crop rotation to the main crop families.l Practice proper sanitation by removing and destroying all crop left-overs atthe end of the season.Cabbage Ecological Guide - 200010

Major Agronomic PracticesOpen pollinated variety: seed produced from natural pollination so that the resulting plants are oftenvaried: they may have characteristics from the mother plant, from the father plant or from a combinationof the two. Seed from OP varieties can often be multiplied by farmers but requires a bit of selection: onlyseed of the best fruits and plants should be used. Depending on the breeding process and the crop,commercial OPs can be very homogenous.3.2.2 Resistant varietiesAnother important aspect to consider when selecting a variety, is if the variety is tolerant or resistantagainst certain insect pests or diseases. Growing a resistant variety is one of the best and mostenvironmental safe methods of crop protection! Unfortunately, resistant varieties are not always available.Also, resistant varieties are usually not resistant to all pests and diseases that may occur.Resistant variety: an insect pest or disease cannotlive on the plant. This can be due to long or stickyhairs on a plant that hinder an insect to walk andfeed on a plant, or the excretion of toxic chemicalsby the plant, or the chemical constitution of the plantsap that make it less attractive to insects or diseases.Tolerant variety: an insect pest or disease can infect the plant butsymptoms will not be severe and the effect on yield will be none orminimal. However, infected plants may become a source of infectionfor other fields.Susceptible variety: insects or diseases can attack the plant and thismay result in yield and quality loss.Test cabbages in a varietal trialMany seed companies are willing to support demonstration plots of different varieties. For the seedcompany, the demonstration plot may be a promotion and they will often provide the seed for free.For farmer groups it may be worth the effort contacting a few companies and testing a number ofvarieties under local conditions. Some varieties may be interesting with regard to suitability to aspecific climate/season, resistance/tolerance to insect pests and diseases, yield or other factors.Make sure to include the locally used varieties for comparison.Cabbage Ecological Guide - 200012

Major Agronomic Practices3.2.3 Seed germinationSeed is of good quality when more than 70% of the seed germinates and germination occurs withinapproximately 7 – 14 days. Irregular germination results in seedlings of different size. High germinationpercentage is important because hybrid seed is often the most expensive input of cabbage production!Good quality seed will also be disease-free.Most seed companies have their own minimum seed germination standards. For example, an internationalseed company based in Thailand states that germination of their hybrid cabbage is over 80%. Actualgermination depends on seed age and storage conditions.Some countries, for example Thailand, have a “Seed Law” which lists minimum germination percentagesfor various crops.Related exercises from CABI Bioscience/FAO manual:2-C.4. Testing of cultivars2-A.10 Test for seed germination3.3 Seed treatmentsThere are two reasons to treat seed:1. to control diseases attached to or inside the seed (seed-borne diseases)2. to protect against diseases in the soil that can attack seed, emerging roots or young seedlings (soilbornediseases)Seed-borne diseasesSeed can become infected with fungal spores or bacteria (seed-borne diseases). Infection can occurduring the growing season, when seed is still on the plant or it may occur after the seed has beenextracted from the plant. Common seed-borne diseases in cabbage are black rot (bacterium Xanthomonascampestris), Alternaria leafspot (fungus Alternaria brassicae) and black leg (fungus Phoma lingam).Most seed companies do not normally treat cabbage seed. Only when a seed-borne infection such asblack rot is suspected, seed lots may be treated (usually hot water treatment, sometimes by treatingseed with diluted hydrochloric acid or sodium phosphate). Other sterilization methods are listed below.Soil-borne diseasesSeed can also become infected after it has been sown in the soil. Fungi or bacteria living in the soil mayattack the seed and cause death of the seed or the emerging roots even before the seedling has emergedabove the soil (soil-borne diseases). A common soil-borne disease affecting seed and seedlings isdamping-off, caused by a complex of fungi. See section 8.1.When to treatWhen seed is bought from reliable seed companies, it will usually be disease-free. When seed is locallyproduced, it is probably better to sterilize it before sowing. When soil has given problems with dampingoffdisease before, it can be helpful (next to cultural practices such as rotation, and possibly soil sterilization,see sections 3.7.1. and 3.12) to coat seed before sowing.13 Cabbage Ecological Guide - 2000

Major Agronomic PracticesHow to treatThere are four main methods for seed treatment:1. Physical: by soaking seed in hot water.2. Chemical: by sterilizing seed with chemicals or by coating seed with a layer of fungicide.3. Botanical: by coating seed with a layer of plant extract.4. Biological: by coating seed with a layer of antagonistic fungi (see also section 7.10).None of these treatments will completely prevent pathogen attack in all circumstances!In addition to seed treatment, it is important to select a field that is free of soil-borne diseases. Somemanagement practices for soil-borne diseases include crop rotation (using soil that has not been usedfor growing cabbage or other cruciferous crops for at least 2 years) and the use of resistant or tolerantcabbage varieties. See also sections 3.2 on variety selection, 3.4 on soil, 3.7 on nursery management,3.12 on crop rotation, and box in section 3.4.3.3.3.1 Hot water seed treatmentTo kill most spores or bacteria attached to or within the seed, seedshould be soaked in hot water at 50 o C for 30 minutes.The right water temperature and the right duration are very important. Ifthe water is too cold, the pathogens are not killed. If the water is too hot,seed germination will be strongly reduced.The easiest way to treat seed is to prepare water of 50 o C on a small fireor burner. Carefully check the water temperature with a thermometer.Poor the 50 o C water into a thermos flask and add the seed. It may beeasy to wrap the seed in a cloth to keep them together. Leave the seedin the flask for 30 minutes. After soaking in hot water, the seed is placedin clean, boiled, cold water to cool down. Dry by spreading the seed ina thin layer on paper or on cloth.In some cases, a fungicide coating is applied after hot-water treatment. See section 3.3.2 below.J Hot-water treatment is easier, cheaper and more effective than tryingto control seed-borne diseases in the field with chemicals. J3.3.2 Chemical seed treatmentMany seed companies use chemical treatments, such as sodium hypochlorite, to sterilize the surface ofthe seed. Next to this, seed can be coated with a fungicide. This fungicide can sometimes be seen onthe seed as a colored coating. The fungicide used will be listed on the seed package. The fungicide cankill spores of diseases that are present on the seed and during germination it gives some protection ofemerging roots to soil-borne diseases. Chemical fungicides for seed protection are relatively inexpensiveand cause little environmental damage since they are used in small amounts. However, they are effectiveonly for a short time (at most one month) and they do not spread through the soil with the root system.Cabbage Ecological Guide - 200014

Major Agronomic PracticesUse protective gloves when planting coated seed !Unfortunately, chemical seed sterilization cannotguarantee that the seed are completely diseasefree. This is because some pathogens are presentwithin the seed. An example is the bacterium blackrot in cabbage. Chemicals only sterilize the surfaceof the seed and do not reach infections inside theseed. Research has shown that hot-water treatmentcan penetrate the seed sufficiently to eradicatebacterial infections inside the seed (Boucher,www24).Layer of fungicideCabbage seedSeed : coated with a fungicide3.3.3 Botanical seed treatmentSeed can be protected from some soil-borne fungi and from cutworms by acoating with a botanical extract such as crushed garlic. Garlic is well knownfor its strong odor which has a repellent effect on insects, or birds, and itcan prevent diseases. See also section 4.11.4 on botanicals. The garlic isthoroughly crushed to obtain juice and pulp. Seed is mixed with this extract.The seed can be immediately sown after this treatment, or left to dry.No “scientific” data are available to compare this method with other seedtreatments but it is a common practice in some areas in Bangladesh (pers.comm. Prof. Ahmad, Plant Pathologist University of Mymensingh, Bangladesh,1998).3.3.4 Biological seed treatmentSeed can also be protected with a coating of biological agents. These are usually antagonistic fungi orbacteria that work against soil-borne pathogens. Examples are the antagonist fungus Trichoderma sp.and the bacterium Bacillus subtilis, which is sometimes mixed with a chemical fungicide for commercialseed treatment. See “The Biopesticide Manual (BCPC, U.K.)” for details.The good thing about using biocontrol agents as seed treatment is that they also provide protection of theroots that emerge from the germinating seed. This is because the antagonists grow and multiply in thearea around the seedling roots. This way they suppress fungi that cause damping-off and root disease.Biological seed protection agents are not yet widely available but research results are promising. Onecurrent problem is that biological agents applied to seed will not remain active during storage of seed(Harman,G.F. et al, 1998; USDA, www25).Related exercises from CABI Bioscience/FAO manual:2-A.10. Test for seed germination2-A.11. Preparing seed for sowing15 Cabbage Ecological Guide - 2000

Major Agronomic Practices3.4 Soil3.4.1 The living soilWhen looking at the soil of a field, it may seem like a lifeless amount of sand and pieces of organicwaste. But in fact the soil is very much alive! Many millions of small organisms live in the soil, most ofthem can only be seen with a microscope. These organisms include small nematodes, earthworms,bacteria, fungi, mites, and spring tails. Little is known about the way all of these organisms interact andrestrain each other. But most of them are harmless to the crop and have a beneficial function in decomposingcrop left-overs and other conversion processes in the soil. Others may serve as food for predators suchas spiders. And some other organisms may be classified as neutrals: they do not damage the crop anddo not have a clear beneficial function in the agro-ecosystem. See also section 3.5.3 on role of microorganisms.The Living Soil : soil contains many small organisms like nematodes, fungi, and small insects.(Picture from Schoubroeck et al, 1989).Soil is living and should stay alive, so it is important to:1. Feed it through regular supply of organic material (=food for microorganisms),2. Protect it from erosion, for example by covering the soil,3. Remove or reduce disturbing factors such as (broad spectrum) pesticides and high dosesof chemical fertilizers.Related exercises from CABI Bioscience/FAO manual:2-A.4. The living soilFor more exercises on living soil, see B. Settles’ manual on the website of Community IPM!Cabbage Ecological Guide - 200016

Major Agronomic Practices3.4.2 Soil typeSoil is made up of a mixture of different-sized particles, sand, silt and clay. In nature sand, silt and clayare almost always mixed together in a great variety of combinations which give the soil its characteristictexture. Terms as sand, sandy loam, loam, clay loam, clay, heavy clay indicate the particle size in thesoil. Light soil is composed largely of sand and the name indicates the ease with which it is worked.Heavy soil is soil which contains large amounts of silt and clay. The name refers to the difficulty ofworking and not to the actual weight of the soil.The term ‘structure’ refers to the arrangement of the different particles into soil aggregates. The microorganismsin the soil are responsible for mixing the soil and building of soil structure. Soil particles arebound together by fungal branches and bacterial gums. These help to bind them into aggregates betweenwhich the air and water holding pores areformed. In the pores between the aggregates the soilair is found, an important source of oxygen for rootHumusrespiration. Like humans, most plants and their rootsneed air (oxygen) for respiration! A good soil structurepermits the movement of water through the soil andTopsoilit facilitates the development of a good root system.A good soil can be compared with a new spongethat can absorb plenty of water.SubsoilThe best part of the soil is the dark layer of topsoil,which takes many years to develop. Topsoil is richin plant nutrients and beneficial soil organisms. Underthe topsoil is the yellow, light brown or reddish subsoilwhich may be more acid and is harder for plants to grow in. Humus is the more or less stable fraction ofthe soil organic matter remaining after decomposition of plant and animal residues. Adding organicmaterial such as well-rotten compost, improves the structure of most soil types including heavy clay andlighter sandy soils. The organic matter should be properly composted (well-rotten).Cruciferous crops grow well in any soil that is well-drained and moisture retentive. On heavy soils, plantsgrow slower but the keeping quality (shelf-life) of the cabbages is usually better.A soil pH of 6 to 6.5 is optimal, although cabbage is sometimes grown at higher pH (pH >7.2) for clubrootcontrol. Lower pH values reduce growth. See section 3.4.5 on soil pH.A good site has not grown any cruciferous crops for at least two years. This reduces the chance of (soilborne)diseases. See section 3.12 on crop rotation.Related exercises from CABI Bioscience/FAO manual:2-A.3. Soil structure and effects on root growth2-A.8. Soil test kits3.4.3 Soil infectionNext to the beneficial decomposers or neutral organisms in the soil, soil may also contain organismsthat are harmful to the crop. These include insects and pathogens like fungi, bacteria and nematodes.Soil-borne pathogens can enter a field in numerous ways. They may be attached to pieces of soil on theroots of seedlings, to soil particles on tools used in several fields, or with bits of soil on your slippers orshoes! They may also be spread with the ground water.17 Cabbage Ecological Guide - 2000

Major Agronomic PracticesP reventing soil-borne diseases: some techniques.Preventing soil-borne diseases is not a single action, there are several factors involved. Some of themain activities include:1. Crop rotation (see section 3.12).2. Use of clean seed (see section 3.3).3. Use of disease-free planting material.4. Sanitation practices such as:· removal and destruction of left-over plant material from previous crop,· removing weeds,· cleaning field tools.5. Increasing soil organic matter content (increasing organic matter of soil can increase microbialactivity, which can lower population densities of soil-borne pathogens (see section 3.5.3).6. Proper water management: mainly providing drainage to keep soil around roots from becomingwaterlogged (see section 3.9).7. Application of antagonistic fungi such as Trichoderma sp. into the soil. See section 7.10.Pathogens are so small that they cannot be seen with the naked eyes. Only when they affect the plantsthey become apparent. At that point, some injury to the plants has already occurred. And, maybe evenmore important, once there is a disease in the soil of the field (soil-borne disease), it is very difficult to getrid of it. Many pathogens can survive for a long time in the soil, even without a host plant! Therefore, it isessential to prevent soil-borne diseases from entering the field and attacking the plants. See box above.3.4.4 Soil sterilizationOnce the soil is infected with a pathogen, there are few options for control/management. The best is toreduce the pathogen population with structural methods like crop rotation or the use of resistant varieties.For smaller field sizes, such as nurseries, it is possible to use certain methods to sterilize soil. Suchmethods include solarization or burning (plant)materials on the soil. These and other methods are describedin section 3.7 on nursery management.It is dangerous to use (non-specific) chemicals for soil sterilization. Such chemicals are not alwayseffective because pathogens may live deep in the soil, or be protected inside plant waste, where chemicalsdo not reach. In addition, residues of pesticides in the soil may cause damage to the next crop andresidues may leach into (ground)water causing death of fish, problems with drinking water, and causedamage to micro-organisms in the soil and the aquatic biosystems in general.New methods, such as biofumigation, for “sterilization” (or control of a soil-borne pathogen) of larger fieldsizes are being studied. Biofumigation refers to the release of certain components (so called “biocides”)by plants that can control soil-borne pests and pathogens. For example, excellent suppression of bacterialwilt (a soil-borne disease attacking solanaceous crops like tomato) by mustard green manures wasobtained in field studies. See 3.7.1.4 and 3.7.1.5 for details on biofumigation and other options forbiological soil sterilization.3.4.5 Soil pHAn important factor in soil is whether it is acid or alkaline. This is given in the form of a pH value. ThesepH values range from 1 to 14. If the pH is less than 7 it means that the soil is acid, and if it is greaterCabbage Ecological Guide - 200018

Major Agronomic Practicesthan 7, the soil is alkaline. Soil with a pH of around 7 is considered to be neutral.Soil pH affects the ability of the soil to release nutrients. If the pH level is too high or too low, nutrients canget “locked up” in the soil chemistry and become unavailable to plants. A pH range of approximately 6to 7 promotes the most ready availability of plant nutrients.Next to this, the pH is important for growth of soil pathogens. Clubroot for example (see section 8.6) ismost harmful in acid soils.The soil pH can also influence plant growth by its effect on activity of beneficial micro-organisms. Bacteriathat decompose soil organic matter are hindered in strong acid soils. This prevents organic matter frombreaking down, resulting in an accumulation of organic matter and the “lock up” of nutrients, particularlynitrogen, that are held in the organic matter.Humus (that comes from the break-down of organic matter such as compost) has an important functionin regulating soil pH. Humus itself is neutral and can absorb acid and alkali shocks from outside. Applicationof lots of organic matter into soils is a good and more permanent solution to neutralize soil pH than theapplication of lime. However, strongly acid soils should also receive lime.Like many vegetables, cabbage is sensitive to acid soils and will perform best in soil with a pH range ofabout 6.0 to 7.0. Cabbage is sometimes grown at higher pH (pH > 7.2) for clubroot control. Lower pHvalues will reduce growth.3.4.6 Measuring and adjusting soil pHThe soil pH can be measured with a pH meter or a soil testing kit which uses chemicals and a colorcomparison to determine the pH of the soil.Soils tend to become acidic as a result of:1. rainwater leaching away basic ions (calcium, magnesium, potassium and sodium),2. carbon dioxide (CO 2) from decomposingorganic matter and root respiration dissolvingin soil water to form a weak organicacid;3. formation of strong organic and inorganicacids, such as nitric and sulfuric acid, fromdecaying organic matter and oxidation ofammonium and sulfur fertilizers. Stronglyacid soils are usually the result of the actionof these strong organic and inorganic acids.The soil pH can be raised by applying lime orlowered by sulfur application.Lime is usually added to acid soils to increasesoil pH. The addition of lime raises soil pH, andprovides two nutrients, calcium and magnesiumto the soil. Lime also makes phosphorus thatis added to the soil more available for plantgrowth and increases the availability of nitrogenby hastening the decomposition of organicmatter.Types of lime:There are several types of lime available toraise pH. Hydrated lime, which is quickacting, should be applied several weeksprior to planting and watered in well to avoidany chances of burning the crop. Crushedlimestone is much slower acting but longerlasting in its effect. It requires a heavierapplication but can be used with lesschance of burning. Dolomite limestone isparticularly good because it contains atrace element magnesium, which is anessential fertilizer element for plants. Woodashes can also increase soil pH.There may be many other types of lime inyour area. Check with the provider how quickit acts and how it should be applied.19 Cabbage Ecological Guide - 2000

Major Agronomic PracticesIt should be noted that the correction of an acid soil is a process that takes time - sometimes a fewyears! It is therefore good to apply lots of organic matter to increase the level of humus in the soil.The timing of lime application is quite critical as it takes a while before the lime decomposes and the pHgoes up. This depends on type of lime used, humidity and temperature. General rule is that lime shouldbe applied about 4 weeks before transplanting and worked into the soil. It is also good to make sure thesoil is moist when applying lime or watered immediately afterwards.The amount of lime needed to correct a soil acidity problem is affected by a number of factors, includingsoil pH, soil type (amount of sand, silt and clay), structure, and amount of organic matter. In addition tosoil variables the crops or plants to be grown influence the amount of lime needed. Some indications aregiven in table 3.4.6Table 3.4.6 Some indicators of lime required to raise pH 6.5 on different soil typesSoil pHLime required (kg/m 2 ) to raise to pH 6.5Soil type: Sand Soil type: Loam Soil type: Clay6.0 0.10 0.17 0.245.5 0.22 0.37 0.495.0 0.32 0.54 0.734.5 0.39 0.73 0.974.0 0.49 0.85 1.12Lime for control of soil-borne diseases?In some areas, lime is applied to the field for disease control. This has only been “scientificallyproven” in case of clubroot control in cabbage. However, lime may change the micro-environment inthe soil somewhat, resulting in changes of the population of micro-organisms, including pathogens.It may also have an effect on general crop health: by raising thepH, other nutrients become available, plants may grow betterand stronger plants can resist diseases better. Set up an experimentto see what the effects of applying lime would be in yoursituation.In Hai Phong province, North Vietnam for example, farmers havetested the effects of applying compost (15 tons/ha) with andwithout crushed lime in the planting hole during transplantingon disease occurrence in tomato. Results indicated that pestand blossom end rot incidence were similar in all treatments,but AESA led to pesticide applications being reduced from 11 in farmers’ practice plots to seven inthe two IPM treatments. Yields were also higher by 37% and 50% for treatments with and withoutlime, respectively. Profits increased from VND 558,000 in the farmers’ practice treatment to VND787,000 in the plus-lime IPM treatment, and VND 1,007,00 in the no-lime IPM treatment (pers.comm. Dr. J.Vos, 1999; and Vos, 2000, www26).Cabbage Ecological Guide - 200020

Major Agronomic Practices3.4.7 Soil conservation and erosion controlMany farmers are concerned about how to keep or restore soil fertility in order to maintain good yields.Very often, the emphasis is on adding nutrients, not so much on protecting soil through soil conservation.Fertilization and soil conservation are actually equally important. Nutrients are linked with chemicalqualities of the soil, conservation also emphasizes the physical and biological characteristics of soil.Conservation is not only keeping soil parts where they are, but also keeping a good soil structure andstimulating the activity of micro-organisms in the soil.Some principles of soil conservation and fertilization (modified from Murakami, 1991):1. Keeping the soil covered.When soil is uncovered, it is easily attacked by rain, wind and sun heat. This is the main cause fordegradation of soil structure and soil erosion. During growth of a crop in the field, the soil can becovered by a mulch (such as rice straw) or a “living mulch” which is a crop that grows together withthe main crop but is not harvested. When no production crop is planted in the field, consider sowinga cover crop. This will keep the soil covered and thus protected from erosion by wind or water and itis a very good way of fertilizing the soil. See section 3.5.3.2.2. Regular supply of organic material to the soil.Adding organic material to soil is essential for good crop production! Organic matter such ascompost can supply all necessary nutrients to plants and it stimulates activity of micro-organisms inthe soil. Micro-organisms help releasing nutrients from organic material in the soil. See section 3.5.3on organic material.3. Vegetation on field or farm boundary areas.Another useful practice is to plant trees and grasses in boundary areas of a farm. Such vegetationprotects soil from run-off by rain and wind, it becomes a source of organic fertilizer, fodder, fuel, food(fruits), or timber and it also acts as a windbreaker. When flowering plants are used, they may attractnatural enemies such as hover flies, and provide shelter for natural enemies such as spiders.4. No use of pesticides on soil.Pesticides disturb the activity of micro-organisms in the soil and may create imbalances in soilfertility.5. No / Low use of chemical fertilizers.When large amounts of organic material are supplied to the soil every year, usually no chemicalfertilizers need to be added. Chemical fertilizers may create an imbalance in the soil ecosystem.They disturb the activity of micro-organisms by adding only a few nutrients. In addition, nutrientsupply has been known to cause disease problems in plants. In some cases it can be good to usea small amount of e.g. nitrogen to push plants through a stressful period such as downy mildewattack in the nursery.6. Building terraces on steep slopes.On steep slopes, building horizontal terraces is a common and good practice to prevent soil erosion.Often, a small “dike” is made (or a row of weeds is allowed) at the border of a terrace. A commonpattern is the following:21 Cabbage Ecological Guide - 2000

Major Agronomic Practices7. Plant along gradient of the slope.On slopes without terraces, it is recommended to plant the rows of vegetables along the gradient ofthe slope. When rows are planted top-down, rain and irrigation water flow down hill and may takenutrients, soil particles and organic matter down. Those valuable matters are then lost for the crop.Also, with water, soil-borne diseases like bacterial wilt can easily spread into the lower parts of thefield.LJTop down planting stimulates erosion....... plant along the gradient of the slope!Related exercises from CABI Bioscience/FAO manual:2-A.2. Soil conservation: why?3.5 Fertilizer managementPlants use nutrients from the soil in order to grow and produce a crop. Nutrientsare also lost through erosion, leaching and immobilization. Fertilizer managementaims at compensating this loss of nutrients by adding fertilizers. This canbe adding organic materials, chemical fertilizers, or a combination. The importanceof using organic fertilizer is strongly emphasized in this guide.A well-balanced amount of available nutrients results in healthy plants. A healthy plant can resist pestsand diseases better. Well-balanced fertilization is not the same as excessive fertilization! For example,too much nitrogen is known to increase disease occurrence in crops! Also, adding too much (chemical)fertilizer may simply be a waste of money. LThe use organic fertilizers such as compost or green manure, which release nutrients slowly, requirescareful planning and consideration of long-term goals such as improving the structure and biologicalactivity of the soil. This requires basic understanding of some of the processes that take place in the soil.The following sections describe some principles of fertilizer management and ways to improve soil structure,fertility and biological activity (ref. www2).3.5.1 Macro and micronutrientsMacronutrients are nitrogen (N), phosphorus (P) and potassium (K). These are nutrients that all plantsneed in relatively large amounts.Secondary nutrients (calcium, sulfur, and magnesium) and micronutrients (boron, copper, iron, manganese,molybdenum and zinc and chlorine) are essential for growth, but required in smaller quantities than N, P,and K. Usually, secondary and micronutrients are lumped together under micronutrients, also calledtrace elements. Addition of micronutrients should be made only when a clear deficiency is indicated,preferably by a soil test analysis. See section 3.5.7 for fertilization needs of cabbage.Cabbage Ecological Guide - 200022

Major Agronomic PracticesSome of the micronutrients are found in the mineral particles of the soil but most come from humus.Humus comes from the break down of organic matter. The micronutrients exist in very complex formsand have to be broken down into simpler forms which the plant roots can absorb. This process iscomparable with the breakdown of leaves in the soil: slowly they will become soft, fall apart into verysmall pieces and eventually disappear. This breakdown process is done by micro-organisms, mainlybacteria that live in the soil. That is why it is important to stimulate the biological activity in the soil: itresults in better soil fertility! To function effectively, the micro-organisms need air, water, neutral soil (pH6 to 7.5) and lots of organic matter.Organic material usually contains both the macro elements N, P and K and micronutrients.3.5.2 Soil testingThe amount of fertilization to be added depends on the amount of nutrients already available in the soil.A soil-testing service can be a good way to find out how much nutrients needs to be added. In somecountries, the Department of Agriculture provides a soil-testing service. There are also portable test kitsthat can examine the main nutrients of the soil. Results and reliability of these portable kits however vary.The test kits are useful to find deficiencies of N, P and K but recommendations for the amount of fertilizerto be added vary, according to local soil conditions.Soil testing usually does not provide information about soil structure, or biological activity, although someestimate of soil organic matter can be included.Past field history should be considered when interpreting soil test results. This is particularly importantwhen past fertilization has been in the form of organic materials, which release nutrients slowly. In thatcase, soil tests may underpredict the amount of soil nutrients actually available to plants over the courseof the entire season (ref. www2).Additional information on possible soil imbalances maybe gained by looking not only at the leaves and topgrowth of the plant, but by carefully digging up a plant,shaking off the soil, and examining the roots for vigorand signs of disease or pest damage. In general rootsgrowing in a fertile soil are more branched than in a poorsoil, and they have a profusion of root hairs. However,the plants must be dug up very carefully to avoid losingthe root hairs. If the roots are growing laterally and arelong and stringy they are searching for nutrients. If theyare long, seem to be searching for something but growvertically, they need water. If they are growing only nearthe surface, the soil is too wet. If they are thick andshort they may be suffering from a toxic element.3.5.3 Role of organic matter and micro-organismsIn general, organic matter additions to a soil will increase its ability to hold nutrients in an available state.Organic matter additions will also increase soil biological activity, and this affects the availability ofnutrients in the soil. Soil that has received organic matter has increased microbial populations and morevaried fungal species than soils receiving chemical fertilizer applications. The long-term objective oforganic matter addition is to build up soil humus. Humus is the more or less stable fraction of the soilorganic matter remaining after decomposition of plant and animal residues.23 Cabbage Ecological Guide - 2000

Major Agronomic PracticesNutrients : Adding organic matter to the soil stimulates the activity of the many small beneficial organismsthat live in the soil. These micro-organisms make nutrients available to plants by producing humus(decomposition) and by releasing nutrients (mineralization). Organic material is food for micro-organismsand these micro-organisms produce food for the crop. The more active micro-organisms, the morehumus and nutrients become available for plants. Soils that are rich in organic matter are a good sourceof nutrients over a long period of time, as the nutrients from the organic material will be released gradually.If sufficient organic matter is supplied regularly to the soil,usually no chemical fertilizers need to be applied.Soil water-holding capacity : also increases when organic materials are incorporated into the soil. This isespecially useful for locations without irrigation facilities.Soil pH : Humus, formed by micro-organisms, has a regulating effect on soil pH. Soils rich in organicmaterial and humus can absorb acid and alkali “shocks”, e.g. caused by application of chemical fertilizers.See section 3.4.5 on soil pH.Soil health : micro-organisms in the soil promote soil health. Species of those micro-organisms mayinclude antagonists such as the fungus Trichoderma that can control several species of fungi that causedamping-off disease in nurseries. Trichoderma occurs naturally in many soils but can also be applied(see section 7.10.1). There are more examples of useful antagonistic organisms occurring naturally insoils.Organic matter can be added using various methods: compost, cover crops, green manure, organicmulch, etc. A number of organic materials are described in the following sections.3.5.3.1 CompostComposting is the most popular practice for improving soil fertility. Composting involves mixing variousorganic materials such as crop waste and manure and leaving it to decompose. The main purpose is tomake raw organic matter into humus, which is an important source of nutrients and is not harmful for thecrop. Mature compost is a brown-black crumbly material, containing humus, dead and living microorganisms,the more resistant parts of the original wastes, and water.C Advantages of compost:l Quick action : the composting process starts very quickly compared with mulch or green manure: inabout 10 days. The whole composting process takes about 3 to 4 months, depending on materialsused (the softer the material, the quicker) and climate (the warmer, the quicker).llGood fertilizer : good compost can be a rich source of macro elements N, P, K and manymicronutrients. In addition, the nutrients are distributed in the soil more evenly than direct application.Nutrients are released over a long period compared to the quick release over a short time of chemicalfertilizers.Uses locally available materials : any plant material or organic waste that will rot down can be usedto prepare compost. It is therefore cheap to produce. Compost allows the use of materials such asdomestic wastes and sawdust that otherwise tie up soil nitrogen.Cabbage Ecological Guide - 200024

Major Agronomic PracticeslllCreates good soil : organic matter improves the soil structure resulting better water holding capacityof the soil, and soil that is easy to work in. It is food for micro-organisms that make nutrientsavailable by producing humus and by releasing nutrients from organic matter. See also section 3.5.3above on role of organic matter.Reduces pathogen populations : pathogens in the organic material are killed when temperaturesduring composting reach 65 o C and weed seeds are destroyed when temperatures reach 80 o C.Nitrogen regulator : compared to use of manure, compost prevents the loss of N through ammoniagas (NH 3) by fixing N into organic forms. However, some N is lost through NH 3when compost isturned. Compost reduces N below levels that cause burning of plants.D Disadvantages of compost:l Large amount of organic matter required : the ideal amount of compost to apply to a field every yearis 20 tons/ha (about 2 kg/m 2 ). If a farmer wants to supply that amount of organic matter through onlycompost, a huge amount of organic matter is needed. It is very difficult to collect such amounts oforganic matter because in some cases, crop left-overs is also used to feed farm animals and manurecan be needed for cooking activities. Therefore, in most cases, it will be best to combine use ofcompost with other fertilization methods such as green manure and mulch.lllNutrient loss : Composting results in loss of nitrogen as ammonia gas (NH 3) when the compost isturned. Also, compost reduces nitrogen availability in comparison to the raw material from which itwas made.Laborious : the process of making compost takes quite a bit of work as it involves collecting material,making the compost pile, turning the compost and carrying the compost to the field. Therefore it isrecommended that most organic matter be returned as mulch and other, unsuitable material be usedfor compost.Compost is not as effective as raw organic matter in improving soil structure. As micro-organismswork to decompose raw organic matter, they excrete gels and slimes that bind soil particles togetherand enhance soil structure.(modified from www1)How to prepare compostThere are many theories about the best way to prepare compost. Good thing to remember is: howeverthe compost is made, it will benefit the soil!The simplest method for composting is to pile up organic domestic and field waste material, finallycovering the pile with a layer of soil and possibly straw for insulation. Although many publications adviselayering of materials, the best way is to thoroughly mix plant materials throughout the pile. Use equalproportions of dry and wet material. Dry material such as straw, sawdust, and corn stalks contain littlewater and decompose slowly but they provide air to the pile. Make sure that woody material is choppedinto smaller pieces for quicker decomposition. Wet material such as fresh weeds, crop residue and freshmanure contain more water and decompose quicker than dry materials. Wet material contains a lot ofnitrogen, and this is food (energy) for micro-organisms. A lot of food stimulates the micro-organisms to“start working” on decomposition quickly.Small micro-organisms inside the pile will become active in breaking down the organic material. Theseorganisms also need water and air so do not press the pile into a very compact pile of material! It is25 Cabbage Ecological Guide - 2000

Major Agronomic Practicesorganic waste materiallayer of soil and strawbranchesA simple compost pilerecommended to build the pile on a layer of branches to provide air from underneath and to allow drainageof the pile during rainfall.Compost startersSome sources sell compost starters or compost activators, which they claim areneeded to start the decomposition process (the heating) in a compost pile or tospeed up the process. Such starters are often composed of high-nitrogen fertilizers,EM supplements, or even of dehydrated bacteria. While high-nitrogen fertilizersmay be helpful, the benefits of adding more bacteria from a package have yet to beproven. All the bacteria and other micro-organisms you need are usually already present in the soilunder the compost pile and, especially, in the material that you add to the pile.There is no need to add compost starters with “special” micro-organisms!If you still want to give your compost pile a “boost”, the best source of micro-organisms is finishedcompost. When fresh planting material (green leaves, grasses) are added, there will be enoughnitrogen for the micro-organisms to start decomposing the compost quickly. Fresh manure is anothergood source of nitrogen and micro-organisms.During decomposition the temperature inside the pile will rise. It is important to stop adding materials tothe pile at some point to let the micro-organisms do their work. Ideal is when the pile is build up in oneday. When you keep adding materials to the pile, it may take a very long time before the compost can beused and the temperature may not have increased enough to kill possible pathogens. Almost all of thecommon pathogens in a compost pile will be killed when the temperature in the whole pile has reached45 to 65 o C. Exceptions are fungi that form thick layered spores such as clubroot (Plasmodiophorabrassicae) and bottom rot (Rhizoctonia solani). Temperatures around 80ºC are needed to kill most weedseed.Compost thermometerFarmers in Hai Phong, Vietnam, have set up several experiments using compost. To test if thecomposting process inside the pile has started, they placed a stick in the pile like a “thermometer”.They take out the stick and when it is warm, the decomposition has started. If the stick is still coldafter 48 hours, decomposition has not started. This means there may be something wrong in thebuilt of the pile (too compact, too moist, etc). The monitoring of the ‘thermometer’ can be continueddaily to check the temperature rise and fall over time to assess when the decomposition is completedor when the pile is ready for turning. A metal rod, placed in the center of the pile, can also be used asthermometer(pers. comm. Dr. J. Vos, 2000).Cabbage Ecological Guide - 200026

Major Agronomic PracticesWhen a compost pile doesnot heat up, the problem iseither the pile is too small, itis too dry, or it needs morenitrogen. This can be solvedby adding green matter.When the compost has afoul smell, it needs more airand less water. Try turningTemperatures of 45-65 o Ckill most of the commonpathogens andpeststhe pile more often or add more bulking materials such as straw or corn stalks.The compost pile should be turned a few times (e.g. once every 3 weeks, two times in total). Turningsupplies air, needed by the micro-organisms, into the center of the pile and speeds the decay. Turningalso mixes material from the outside of the pile into the hot center. When the compost is dry, it can bewatered after turning. Cover the pile during rainy periods so it will not get too wet.Compost piles can best be sited in a shady sheltered place to give protection from sun and wind.Cover the pile during rainy periods so it will not get too wet.Temperature rising in a freestanding compost heapIt is also possible to dig a pit and pile organic waste material in the pit. This may be especially usefulduring the dry season, when the pile inside a pit will remain moister than on flat soil.A compost pile can be of any size as long as it is easy to handle: it will shrink considerably whiledecomposing. A common recommendation is a pile measuring at least 1 meter in each direction (high,wide and long). A smaller pile will not generate or retain enough heat to effectively kill any harmfulpathogens present.It takes about 3 to 4 months for decomposition to be complete, depending on the climate (the warmer,the quicker) and the contents of the pile (the softer and finer the pieces of the material, the quicker).Compost is ready to use when the pile no longer heats when turned, and the material looks dark andcrumbly.Compost should be sufficiently mature before it is applied. If the original hard parts are still there, thecompost is not mature. The breakdown of immature compost and directly incorporated materials will usenutrients in the soil, which no longer become available for the crop. In addition, immature compost maystill contain pathogens and weed seed. By adding immature compost to the field, you may actually adddiseases and weeds….!L(refs: www30; www31; www32)Disease control with compostAn additional benefit of using compost is that it can reduce disease problems for plants. This is beingstudied for several years now because it offers an opportunity to further reduce fungicide use.Pathologists describe two different types of disease suppression in compost and soil.1) General suppression is due to many different micro-organisms in the compost that either competewith pathogens for nutrients and/or produce certain substances (called antibiotics) that reduce pathogensurvival and growth. Thus an active population of micro-organisms in the soil or compostoutcompetes pathogens and will often prevent disease.This type of suppression is effective on those pathogens that have small propagule (e.g. spores) size.Small spores do not contain many nutrients so for germination they need an external energy (carbon)source. Examples of this mechanism are suppression of damping-off and root rot diseases causedby Pythium species and Phytophthora species.27 Cabbage Ecological Guide - 2000

Major Agronomic Practices2) Specific suppression, on the other hand, is usually explained by one or a few organisms. They exerthyperparasitism on the pathogen or induce systemic resistance in the plant to specific pathogens,much like a vaccination. With specific suppression, the causal agent can be clearly transferred fromone soil to another. Pathogens such as Rhizoctonia solani and Sclerotium rolfsii are examples wherespecific suppression may work but general suppression does not work. This is because these organismshave large propagules (e.g. spores) that are less reliant on external energy and nutrients and thusless susceptible to microbial competition. Specific hyperparasites such as the fungi Trichoderma andGliocladium species will colonize the propagules and reduce disease potential (ref. www33).Other biocontrol agents (or antagonists : for more information see section 7.10 ) that colonize compostsinclude bacteria like Bacillus, Enterobacter, Flavobacterium balusstinum, and Pseudomonas;actinomycetes like Streptomyces.These antagonists may appear naturally in compost. In some cases, antagonistic fungi or bacteria areadded to the compost just after the hot phase, when the compost is cooling down. There are not manymicro-organisms present inside the compost at that moment. When antagonists are added at that time,they can quickly build up their populations and this will result in compost with good disease suppressingquality. See box below.Fortified compostsAn interesting option is the use of fortified compost. This is compost added with antagonistic organismssuch as Trichoderma species (especially T. hamatum and T. harzianum) whereby Trichoderma worksas a compost process enhancer. Such fortified composts provide both nutrients to the crop (throughthe composts) and they provide effective control of a range of plant pathogens (mainly through theantagonistic fungi). After the primary heating period of composting is complete, the Trichoderma isadded to the compost. The fungi increase to high levels in the compost and can effectively reducediseases caused by Rhizoctonia solani, and species of Pythium, Phytophthora and Fusarium. In theUSA, fortified composts must be officially registered.In order for compost to substitute for currently used fungicides, the disease suppressive charactermust be consistent and somewhat quantifiable to reduce risk for the farmers. There are specializedcompost companies that produce consistently suppressive composts, especially for the nurseryindustry.Compost quality plays a role in the degree of disease suppression and the length of suppressive activity.Some general observations:Composts that are allowed to mature are more suppressive than piles used straight after the hot phase.Compost piles that are in the open (so exposed to naturally occurring micro-organisms), and especiallythose located near trees, are more suppressive than compost piles sheltered by a roof.Professional nursery industries now use disease suppressing composts widely and routinely. Based onthe successes there, researchers are testing compost on a number of field crops for potential diseasesuppression. Results of several studies are very promising.For example, studies in California, U.S.A., showed that soils on organic farms (using lots of compost)were more suppressive to two tomato diseases than soils from conventionally managed farms, due todifferences in soil organic matter, population of micro-organism, and nitrate level.Other researchers report less disease incidence (even foliar disease such as early blight in tomato),dramatic reduction in rootknot nematode damage, and higher yields on composted plots compared toconventional treatment in several crops.Cabbage Ecological Guide - 200028

Major Agronomic PracticesIn addition, several researchers are testing the use of compost teas as a foliar spray to prevent andcontrol leaf diseases. See box below.Compost extractsThese are liquid extracts of compost, also called compost teas. Compost teas look rather promisingas preventative sprays to suppress certain leaf diseases, and as method to restore or enhance thepopulation of micro-organisms in the soil.A number of researcher report that compost extracts were effective in the control of diseases suchas late blight (Phytophthora infestans) of potato and tomato, Fusarium wilt (Fusarium oxysporum),and gray mold (Botrytis cinerea) in beans.Compost extracts enable biocontrol of plant pathogens through their action on the leaf surface andon micro-organisms that are present there. A wide range of mechanisms, such as induced resistance,inhibition of spore germination, antagonism, and competition with pathogens, seem to contribute tothe suppressive effect.Factors influencing the efficacy of compost extracts include: age of compost; source of compost(animal manure based composts retain activity longer than composts solely of plant origin); type oftarget pathogen; method of preparation; mode, timing and frequency of application; and meteorologicalconditions. The efficacy of compost extracts can be enhanced by adding beneficial micro-organisms.The methods by which compost watery extracts are prepared are changing as growers and researcherstry new methods. One method is to cover compost with tap water at a ratio between 1:5 to 1:8(volume/volume). This mixture is stirred once and allowed to ferment outdoors. After a soaking period(called “extraction time”) the solution is strained through cloth and then applied with ordinary sprayers.Extraction periods ranged from 2 to 21 days, although most were between 3 to 7 days (at temperateconditions with outside temperature between 15° and 20°C) (ref. www34).Farmers can use farm-produced composts to experiment with extracting teas, and test its effects ondiseases.How to use compostAs most vegetables grow best on soils rich in organic matter, compost can always beadded as much as possible to the field before planting. Ideal would be 20 tons/ha or 2 kgper square meter of land (1 kg is about as much as you can hold in two hands). In Nepal,the recommendation is to use 30 tons/ha.It is recommended to mix the compost into the soil about 2 to 4 weeks before planting. Thiswill give time for the micro-organisms to break down the parts of the compost so that thenutritional elements will be available once the seedlings are transplanted. Also some competition withpossible pathogens in the soil may have occurred. Compost can also be added to the planting holeduring transplanting.3.5.3.2 Cover crops / Green manure / Living mulchCover crops are crops planted to improve the soil, for weed control, erosion preventionor for lowering moisture loss (during hot season) rather than for harvest. Such cropsare also often called “green manure” or “living mulch” although strictly speaking, theterms are slightly different. Cover crops and green manure are usually grown when29 Cabbage Ecological Guide - 2000

Major Agronomic Practicesthe land is fallow whereas living mulch can be grown together with the crop. Living mulch is usually aleguminous crop, such as clover or pea grass, which remains low, covers a wide area, and is long lastingas it is being grown over several seasons.Cover crops can gradually add organic matter to the soil and help retain soil nutrients from one season tothe next. The contribution to soil organic matter and soil fertility varies with the kind of cover crop used.For example, legumes decay quickly because residues are high in nitrogen. Therefore, they are morevaluable as N sources than as organic matter sources. Grass crops, such as rye or jute, will have amuch greater effect on soil organic matter content than legumes because they have a higher carbon tonitrogen (C:N) ratio and decay more slowly.For a cover crop to be an effective fertilizer, it must also accumulate nutrients that would not otherwise beavailable to the following crop. Legume cover crops supply some or most of the following crop’s nitrogenneeds, but some other cover crops also increase plant nutrient availability. For example, buckwheat andsweet clover are able to accumulate phosphorus even in soils with low available phosphorus. Others mayhave root systems that go deeply into the soil. The decaying year after year of these deep roots leavesstores of organic matter into the soil. This type of deep fertilization cannot be duplicated in any other formso cheaply and easily! In general, cover crops need to be incorporated to speed up nutrient availability tothe following crop (Peet, www5).Green manure is a crop (often a legume crop) planted during a fallow period, grown for several weeks,then ploughed into the soil. About 2 –3 weeks is given to allow decomposing of the green manure crop.After that, the main crop, e.g. cabbage, can be planted into the field.Green manure has some advantage over usual compost in that it supplies the soil with organic matter atthe peak of its nutritional benefit. Compost will loose some of its nutrients due to leaching and otheractions of the elements. Green manure is a very effective method to supply a lot of organic matter to thesoil without having to collect it from outside (such as in case of compost). Disadvantage is that severalweeks are involved to produce it, during which the land cannot be used for other crops.Some examples of crops that can be used as green manure/cover crops:l alfalfa l cloversl cowpea, grass pea, sweet pea l soybean, mung bean, velvet beanThese are all nitrogen-fixing crops. The roots of these plants fix nitrogen from the air into the soil,releasing it slowly to following crops.Decomposition of green manure cropsAfter green manure crops have been turned in, the plant tissue starts to decompose. It becomes softand slowly, it falls into small pieces. It is important to allow time for decomposition, before plantingthe main crop because:l Decomposition process will consume oxygen from the soil, this oxygen is also needed by plantroots.l Decomposition process produces methane, a gas harmful to plant roots.An exception to this is when green manure crops are grown to suppress certain soil-borne diseases,as a kind of biological soil sterilization. Details of such methods can be found in section 3.7.1.4 and3.7.1.4.Time needed for complete decomposition can be about 3 weeks for legume crops. Exact timedepends on temperature, soil moisture, and kind of green manure crop. See also section 3.5.3.3 onmanure.Cabbage Ecological Guide - 200030

Major Agronomic PracticesSome farmers use weeds as green manure. They work the weeds into the soil when preparing the field fortransplanting. This is easier than sowing a separate manure crop but has certain risks: when the weedsbear flowers and seed you actually sow weeds! And some weeds have long rootstocks which when cutinto pieces during the ploughing, will each give a new weed plant. This may eventually lead to moreweeds. Most weeds do not fix nitrogen. In addition, some weeds can be hosts for cabbage diseases,particularly weeds that belong to the family of Cruciferae. L(modified from www1)Related exercises from CABI Bioscience/FAO manual:2-A.5. Use of green manure3.5.3.3 ManureManure, like composted materials, is used to add nutrients (manure can be especially rich inmicronutrients), improve the water-holding capacity of soils and to improve the structural stability ofheavy soils. Total benefits from manure sometimes take three or more years to become apparent. This isbecause a portion of the nutrients and organic matter in manure is broken down and released during thefirst year or two, but a portion is also held in humus-like compounds which decompose more slowly.Determining the correct amount of manure to apply is difficult. Manure samples should be analyzed fornutrient content and levels of metals such as copper, which are often present in poultry litter and pigmanure. Nitrogen available to the plant is lower than the content in the samples since some loss occursthrough volatilization (through ammonia gas NH 3) with spreading and since only a portion of the organicN becomes available to the plants through mineralization during the growing season. Also, the rate ofmanure application needed to supply the nitrogen needs of the crop will usually supply phosphorus andpotassium in amounts in excess of those the plant can use. This excess application generally does notaffect crop growth but can, in the case of phosphorus, pollute water if runoff or erosion occurs. Phosphorusrunoff can be minimized by controlling erosion with cover crops or mulches (Peet, www11 and www1).Average nutrients available in manure from different sources, and from ashes are listed below .Table 3.5.3.3 : Average nutrients available in manureType of Nitrogen (N) Phosphoric acid (P 2O 5) Potash (K 2O)manure (%) (%) (%)cattle dung, fresh 0.3 – 0.4 0.1 – 0.2 0.1 – 0.3horse dung, fresh 0.4 – 0.5 0.3 – 0.4 0.3 – 0.4poultry manure, fresh 1.0 – 1.8 1.4 – 1.8 0.8 – 0.9cattle urine 0.9 – 1.2 trace 0.5 – 1.0horse urine 1.2 – 1.5 trace 1.3 – 1.5human urine 0.6 – 1.0 0.1 – 0.2 0.2 – 0.3Farmyard manure, dry 0.4 – 1.5 0.3 – 0.9 0.3 – 1.9Ash, coal 0.7 0.5 0.5Ash, household 0.5 – 1.9 1.6 – 4.2 2.3 – 12.0(Tata, S.N, 1992, ICAR, Handbook of Agriculture, India).31 Cabbage Ecological Guide - 2000

Major Agronomic PracticesIn general, direct application of manure or other raw animal wastes is not recommended. Main reasonsinclude:lllllllFresh manure may contain diseases that tolerate the digestive passage (such as spores of clubrootin cabbage) and may contain insect larvae such as maggots which can destroy roots of cabbageplants. In fact, decaying manure attracts insects such as cabbage maggot adults for egg laying.Uncomposted manures are difficult to apply, not only because of their bulk, but because it is easy toapply more nitrogen than the plants can absorb. Too much nitrogen in cabbage may result in long,stretched plants which fall over easily.Direct application can lead to problems of excess nitrates in the plant and runoff of nitrates intosurrounding water supplies.Excessive raw manure can burn plants and lead to toxic levels of nitrates in leafy greens.Decomposition process will consume oxygen from the soil; this oxygen is also needed by plantroots. One case where this process may be tolerable is described in section 3.7.1 on soil sterilizationof nurseries.Decomposition process produces methane, a gas harmful to plant roots. Also see section 3.7.1 onsoil sterilization of nurseries.Regular supply of fresh manure leads to lower soil pH.3.5.3.4 Organic mulchesMulch is any material placed on the soil surface to protect the soil from the adverse effects of rainfall,wind, and water loss. Mulches are also used to control weeds and reduce erosion. Organic mulchingmaterials will break down over time, contributing organic matter to the soil. The use of mulches for weedcontrol is discussed further in chapter 9 on Weed Management.Furthermore, as mulch reduces the need for tillage, plowing labor is reduced.Many kinds of organic materials can be used as mulch including tree leaves, grasses, crop residues (butonly those free of diseases and insect pests!), saw dust, rice straw, etc. Even weeds (without seeds),coconut leaves, water hyacinths and compost can be used as mulch.When selecting mulch material, it is important to consider your requirements and the characteristics ofthe material. For soil protection the use of high Carbo/Nitrogen (C/N) ratio (high carbon content: usually“dry” materials) material are recommended. Examples of high C/N ratio materials are straw, lemongrasses and coconut leaves. These last for a long time. For soil fertilization purposes, low C/N ratiomaterial (high nitrogen content: usually “wet” materials) are recommended. Examples are leguminousgrasses, leguminous crops, and compost.Leguminous crops, such as clovers, can also be grown as a “living mulch”, grown together with the maincrop. Such living mulch is an effective soil protection and it provides nitrogen to the main crop. Seesection 3.5.3 above and box below.Cabbage Ecological Guide - 200032

Major Agronomic PracticesEffects of undersowing with clover on pest insect occurrenceVarious studies report that when cabbage is intercropped with clover, fewer pest insects are found oncabbage plants in clover than on those in bare soil. The insect species reduced vary in every publicationbut in several studies, fewer flea beetles (Phyllotreta sp.), Pieris sp. and cabbage aphids (Brevicorynebrassicae) are mentioned. Some studies report reduction of diamondback moth (Plutella xylostella)but this is not consistent.The number of natural enemies is usually higher in the undersown plots; especially syrphid flies andcaterpillar parasitoids are found. JA reduction in the weight of the cabbage heads is also regularly mentioned in the studies. L(Wiech, 1993; Wiech, 1996)However, a study from the Netherlands reported that although no pesticides were used and competitionreduced cabbage head weight, the better quality of the intercropped cabbages (due to less pestinjury) lead to a better financial result compared with the monocropped cabbage.(Theunissen, J. et al, 1995)3.5.4 Chemical fertilizersInorganic or chemical fertilizersare usually added for the short-term food needs ofthe plants.The three main elements in chemical fertilizers are nitrogen (N), phosphorus (P),and potassium (K). Chemical fertilizers can usually be bought separately or in acombination with different proportions. A combination of the three fertilizers isdescribed by a series of three numbers referring to the content of each element. For example: 25-15-5means the fertilizer contains 25% N, 15% P and 5% K.Some micronutrients such as boron can be bought separately; however, additions of micronutrientsshould be made only when a deficiency is indicated, preferably by a soil test analysis.3.5.5 Comparing organic and chemical fertilizersWhen comparing organic and chemical fertilizers on the amount of nutrients they contain, the followingpoints must be kept in mind:lllOrganic fertilizers such as compost vary widely in composition depending on the raw material used intheir preparation.Organic fertilizers usually provide (part of) the major plant nutrients N, P and K , and a wide range ofmicronutrients, whereas chemical fertilizers do not.Nutrients are normally more slowly released from composts than from very water-soluble chemicalfertilizers. This means the crop will profit longer from organic compost, especially during the rainyseason. Some nutrients in compost are held in humus-like compounds which decompose very slowlyso that their effects on soil continue for years after application.33 Cabbage Ecological Guide - 2000

Major Agronomic PracticesIn the table below a list of the advantages and disadvantages of both fertilizers is given:Table 3.5.5 : Comparing organic and chemical fertilizersAdvantageDisadvantageOrganic fertilizer• rich in nutrients• usually provide (part of) the micronutrientsN, P & K, and wide range of micronutrients• improves soil structure• increases water holding capacity soil• gradual release of nutrients• improves nutrient exchange system• stimulates activity of micro-organisms thatmake nutrients from the soil available toplants• organic fertilizers such as compost verywidely in composition depending on theraw material used in their preparationChemical fertilizer• high content of a fewnutrients per volume unit (kg)• fast release of nutrients• easy to determine dosage• easy to apply, not labourintensive• usually very water soluble,may be washedaway/drained off quicklyduring wet season• expensive3.5.6 Foliar fertilizersIn some areas, farmers make use of foliar fertilizers. These are solutions of fertilizers that are sprayed onthe leaves of the plant. The advantage of using foliar fertilizer is that it is quickly taken up by the plant,quicker than the nutrient uptake from organic or inorganic fertilizers by the roots. They can be used as acorrective measure for example when a deficiency of a certain nutritional element is discovered. Adisadvantage is that foliar fertilizers are expensive and act very short term - no gradual release of nutrients,no effect on soil structure. And, when not used correctly, foliar fertilizers may cause burning of theleaves. Also, some pest and diseases can become more serious when crops are too generously fertilized.Field studies with foliar fertilizers in Dalat and Hanoi (Vietnam) showed a slight increase in yield but theeconomic efficiency was not clear (FAO- Updates on Vietnam national IPM programme in vegetables, 1999).To see if foliar fertilizers would be economical for use in your field, compare a small area with foliarfertilizers with an area in which common fertilization is used. Note down cost of fertilizers, incidence ofinsect pests and diseases and economic returns.3.5.7 Fertilization needs of cabbageAn indication for the amount of organic and inorganic fertilizers for cabbage are given in the table below.These guidelines are very general and the range in doses for the fertilizers is broad. The exact dosage tobe applied depend on the nutrients already available in the soil (soil test service, see 3.5.2), soil type andstructure, environment, etc. It is recommended to prefer organic above inorganic (chemical) fertilizers!When lots of organic matter is used regularly, the doses of chemical fertilizers can usually be (very) low,a lot lower than indicated in the table!It is recommended to set up a field study to test different types and doses of fertilizers to check the bestcombination for your crop and field situation. In Dalat and Hanoi, Vietnam, for example, cabbage fieldstudies showed that chemical fertilizers alone were not sufficient for good plant development. It was alsoadvised to include proper economic analysis in field experiments as some of the organic fertilizer wasexpensive when bought from elsewhere. (FAO - Updates on Vietnam Nat. IPM programme in vegetables, 1999).Cabbage Ecological Guide - 200034

Major Agronomic PracticesAn example of a recommendation for total application of fertilizers for cabbage is:Table 3.5.7 : An example of a fertilizer recommendation for cabbageFertilizer Total dose Split applications Method TimingCompost 15 – 20 tons/ha no Mixed intoplanting holes• Before/attransplantingNitrogen(N)100 – 170 kg/ha 60 – 85 kg/ha20 – 60 kg/haBroadcastedSide-dressed• Before transplantingAt 14 to 21 DAT20 – 60 kg/ha Side-dressed • If needed – at earlyhead developmentPhosphorous(P 2 O 5 )60 – 150 kg/ha 30 – 80 kg/ha30 – 70 kg/haBroadcastedSide-dressed• Before transplanting• At 14 to 21 DATPotassium(K 2 O)60 – 225 kg/ha 35 – 170 kg/ha25 – 55 kg/haBroadcastedSide-dressed• Before transplanting• At 14 to 21 DATBoron 2 – 3 kg/ha no Broadcasted • At transplanting(modified from FAO, 1988; Peet, www5; and pers. comm. IPM trainers Hanoi, Vietnam, 2000)Part of the recommended nutrients can have organic sources, such as compost or green manure. Seesection 3.5.3.Every person, every book or guide will give another recommendation forcabbage fertilization. The only way to determine the best type, amount, timingand application techniques of fertilization for your area, your field, your crop, is toexperiment !The effects of N, P, K and boron in cabbageNitrogen (N) promotes vegetative growth. Like most leafy vegetables, cabbageneeds a lot of nitrogen. Too little nitrogen reduces yields, delays maturity, andshortens storage life. Too rapid growth at high nitrogen, however, can lead to coarse,loose heads, cracking, tipburn, and poor processing and storage quality.The application of too much nitrogen (urea) however, may result in a high percentage of nitrate in theleaves of the cabbages which is detrimental to the human health.An excess of potassium (K) can cause the heads to burst and a deficiency of potash can result innecrosis at the margins of the leaves and a reduction in the keeping quality of the heads.High level of phosphorus (P) throughout the root zone is essential for rapid root development and forgood utilization of water and other nutrients by the plants.Be aware that both P and K are being released slowly, and that particularly P is needed for rootdevelopment, therefore basal application of P and K is crucial for healthy crop development. TopdressingP and K is often not efficient.Cabbage has a high boron requirement. Symptoms of boron deficiency vary with the cole cropattacked. Cabbage heads may be small and yellow. Most cole crops develop cracked and corkystems, petioles and midribs. The stems of broccoli, cabbage and cauliflower can be hollow and aresometimes discolored. Cauliflower curds become brown and leaves may roll and curl. If boron isadded, and beans or other boron sensitive crops follow cabbage in a rotation, a soil test is advisablebefore planting to ensure that boron levels are not too high.(Peet, www3)35 Cabbage Ecological Guide - 2000

Major Agronomic PracticesRelated exercises from CABI Bioscience/FAO manual:2-C.5. Fertilizing experiments2-C.6. Use of foliar fertilizers2-A.6. Composting2-A.7. Use of compost3.6 Planting time and pest occurrenceThe type and number of pest and diseases can vary in different times during the year. During the dryseason for example, there will usually be less problems with diseases. Knowing when a pest or diseaseis most severe can offer an opportunity to plant the crop during the time that pests and disease are notpresent in large numbers or just before that time. That gives the plant the opportunity to be well establishedin the field before an attack by an insect or a disease occurs.Planting time and insects, an example from Lao PDR:During the cool season in Lao PDR, October to January, there are no major problemswith pests or diseases of cabbage. From February onwards, the temperature rises and pests suchas diamondback moth (Plutella xylostella) and webworm (Hellula undalis) become a problem.Related exercises from CABI Bioscience/FAO manual:2-A.12. Weather conditions and planting time3.7 Nursery management3.7.1 Soil sterilizationThere are several ways of sterilizing soil, both as a preventive measure against soil-borne diseases (suchas damping-off) and as a method to control soil-borne diseases already present. A number of commonpractices is shortly described below.To see if any of these soil sterilization methods work in your field, set up a study to compare this methodagainst the common practice!3.7.1.1 Burning organic material on the soilA common method of soil sterilization is heating up the soil. The high temperature will cause the deathof many micro-organisms, including pathogens in the top soil and insect pest with soil-dwelling stages,such as cutworms. In Bangladesh, Nepal and India, for example, soil sterilization is commonly practicedby burning straw, or dry grass, leaves or waste material on the nursery beds before sowing. It should benoted that straw burns very shortly and the heat does not penetrate deep enough into the soil. This mayresult in only a very thin top layer of the soil being sterilized. A substantial amount of slow-burning buthigh-temperature output material would be required on the soil, e.g. wood rather than grass (Bridge,1996). Rice husk is preferred to straw because it burns slower and the heat penetrates deeper into thesoil, resulting in better sterilization.In Bangladesh, Choudhury and Hoque (1982) demonstrated that by burning a 5-cm thick layer of ricehusks (burnt in 90 min) and a 5-cm thick layer of sawdust (burnt in 60 min) on the surface of vegetableCabbage Ecological Guide - 200036

Major Agronomic Practicesseed beds, root-knot nematode galls on the following crop of eggplant were reduced to 23 and 37%,respectively, of the number of galls on roots in non-treated seed beds. A 15-cm thick layer of rice straw(burnt in 20 min) however only reduced galling to 50% of the control plots.Soil from fire placeAnother example of an alternative method of soil sterilization came from Bangladesh, where a farmerused the soil from his fire place to prepare a nursery. This soil had been heated several times over along period for cooking activities. The heat had killed pathogens in the soil. It would be advisable tomix the soil with compost before sowing seed.(pers. comm. farmer Chittagong, Bangladesh, 1998)3.7.1.2 SolarizationAnother soil sterilization method is solarization - with help of the sun. Solarization of seedbeds cancontrol soil-borne diseases, weed seeds and some nematodes including rootknot nematodes. However,not all pests are controlledTo solarize soil, the soil is covered with clear polythene/plastic sheets. The best time is during the hotseason, when there is plenty of sun. The sun heats the soil through the plastic and the plastic sheetkeeps the heat inside the soil. Usually, the sheets should be left on the soil for at least 4 weeks,depending on the season (hours of sunshine and temperature) and the area (lowland or highlands). Thesoil should be wet before the plastic sheets are placed and the sheets should be properly fixed on thesides to avoid loosing heat. Also check the polythene sheets for holes and repair them where necessary.Ploughing the soil before applying the plastic sheets seems to help to break up crop left-overs and bringnematodes to the surface so the heat can destroy them. Allow the soil to cool down for at least a fewdays before sowing seed.plastic sheet, fixedwith soil at thebordersSolarization : the sun heats up the soil under the plastic sheetand kills insects, diseases and some weeds.It should be noted that polythene sheets may be expensive, and when no longer usable, they may createenvironmental pollution.Solarization can be combined with another soil sterilization method described in section 3.7.1.5. Withthis method a large amount of organic material (e.g. a green manure crop like grass (40 tons/ha)) isincorporated into the soil before applying the plastic sheets. A better sterilization effect may be obtainedand organic material is added to the soil, which improves soil structure and fertilization. See section3.7.1.5 for details.37 Cabbage Ecological Guide - 2000

Major Agronomic Practices3.7.1.3 Use of sub-soilWhen damping-off disease is a problem in an area, and there is no possibility to shift the nursery toanother site, the use of sub-soil may be an alternative to reduce the chance of damping-off disease. Thismethod is practiced in parts of Indonesia with very good results. Most of the damping-off causing organismslive in the top layer of the soil. Remove the top layer of about 30 cm in an area close to the nursery siteand dig out the soil below this layer. This soil is used to prepare the raised nursery bed. It is recommendedto mix the sub-soil with some compost.top soil is removed,..to prepare raised nursery beds.sub soil is used....3.7.1.4 BiofumigationSoil-borne pests and pathogens can be suppressed by chemical compounds that are released duringdecomposition of certain crops. This is called biofumigation. The chemical compounds that are able tokill or suppress pathogens are principally isothiocyanates. Those crops with biofumigation potential areused as a rotation crop, a companion or a green manure crop. In Australia, research is ongoing to testwhich crops can be used for suppression of certain pests and pathogens (pers. comm. Dr. John Kirkegaard,1999).At present excellent suppression of bacterial wilt of solanaceous crops (tomato, eggplant, etc.) bymustard green manures has been achieved while for other pathogens (e.g. Pythium sp. causing damping-offdisease) the effectiveness is poor.3.7.1.5 Biological soil sterilizationAnother relatively new method of soil sterilization, comparable with biofumigation (see section above) isbeing studied where soil sterilization is achieved by naturally present organisms in the soil. It requiresair-tight plastic sheets. Fresh plant material (from previous crop or a green manure crop) is worked intothe soil deep and homogeneously. The field is watered and covered with an air-tight plastic sheet (0.12-0.15 mm thick), properly fixed at all sides. The sheet is left on the field for 6 – 8 weeks (Note: studyresults from temperate (Dutch) climatic conditions).Within a few days of applying the plastic sheet, the oxygen in the soil is gone. The oxygen is used bymicro-organisms in the soil. Without oxygen, the micro-organisms cannot break down the organic materialthe usual way (into carbon (CO 2and water (H 2O)) so they switch to fermentation. During this fermentation,several degradation products are formed and after some time, a biogas, methane, is formed in addition.Also, the concentration of carbon in the soil increases. The fermentation products, the biogas methaneand the carbon are thought to play an important role in the suppression of some soil pathogens andnematodes. The effects are better at higher temperatures.In small scale field trials in the Netherlands, the effect of this method was studied on survival of the soilbornepathogen Fusarium oxysporum. The organic matter used was grass (40 tons/ha) or broccoli.Results showed that good control was achieved in the soil layer where plant material was present. BelowCabbage Ecological Guide - 200038

Major Agronomic Practicesthis layer, the effect disappeared. It is planned to test the method on larger scale production fields.Similar studies showed that biological soil sterilization was effective against the fungi Fusarium oxysporum,Rhizoctonia solani and R. tuliparum, Verticillium dahliae, Sclerotinia sclerotiorum and different nematodespecies (Meloidogyne and Pratyenchus).This soil sterilization method can be combined with solarization (see section 3.7.1.2). Under the Dutchtemperate conditions (with low amount of sunshine), the plastic used was non-transparent to preventweeds from germinating under the plastic and produce oxygen, thus reducing the sterilization effect.However, when using transparent plastic under tropical conditions, the expectation is that the soiltemperature rises enough to kill weed seeds. When incorporating organic matter into the soil beforeplacing the plastic sheets, three effects may be obtained:lllsoil sterilization by fermentation processes caused by degradation of organic material by microorganismsunder anaerobic (no oxygen available) conditions,soil sterilization by rise of soil temperature due to sunshine and plastic sheets,addition of organic material through the green manure crop to improve soil structure and soil fertilization.(Blok, PAGV Jaarverslag 1998; pers. comm. Dr. W. Blok, Wageningen Agr.Univ., 1999).3.7.1.6 Boiled waterAlthough not “scientifically proven” the use of boiling water for soil sterilization may be an option for soilsterilization. A farmer from Bangladesh used this method: he boiled water and poured it one to threetimes over the nursery soil to kill pathogens and possibly insects and/or nematodes in the seedbed. Helet the soil drain and cool down before sowing the seed (pers.comm. Chittagong farmer Bangladesh).It would however be advisable to set up an experiment (possibly with pot trials) to test if this methodwould be appropriate for your area.“ ’’To see if any of these soil sterilization methods work in your field,set up a study to compare the method against the common practice!3.7.2 SowingCabbage can be sown directly in the field or sown in a nursery and transplanted later. Usually, cabbageis sown in a nursery. This nursery should ideally be located at a sunny place where the soil is not toowet. High humidity may provoke diseases like damping-off which can destroy seedlings in a very shorttime. If possible, the nursery should be sited on land which has not grown cruciferous crops like cabbage,cauliflower, or broccoli for 3 years or more. This is a prevention for the occurrence of (soil-borne) diseases.3.7.2.1 Flat field and raised seedbedsProper drainage and aeration are necessary to prevent soil-borne diseases like damping-off. A goodoption is to prepare raised seedbeds which will dry more quickly than flat-field plantings.Compost can be mixed in the seedbeds to get a fine soil structure with sufficient nutrients. Compost mayalso help prevent damping-off. See section 3.5.3.1. Make sure the seedbeds are properly leveled. Digtrenches between the seedbeds to facilitate drainage of the nursery.39 Cabbage Ecological Guide - 2000

Major Agronomic Practicesrows with tomato seedraised seedbedSeed is sown about 1.5 - 2 cm deep in rows at a spacing of about 2.5 cm between the plants and 30 cmbetween the rows. Seed is either broadcast in rows and thinned out later or placed individually every 2.5cm. If the seed is placed deeper, it will take more time to germinate, so it takes longer before seedlingsare ready for transplanting. When seed is sown less than about 1 cm deep, it will be more susceptible todrought, and will form weaker seedlings.Broadcasting the whole seedbed usually costs a lot of seed and results in irregular patches of seedlingswhich need to be thinned out to obtain strong seedlings.Precision sowing: inspiration from Jessore, Bangladesh:A farmer from Jessore sows his eggplant nursery with help of a wooden frame with small pins whichhe places on the soil of the nursery beds. The pins make small holes in the soil at equal intervals toindicate the positions of the seed. He then sows 2 to 3 seeds in each hole. With this method ofprecision sowing, this farmer was able to get a good nursery with a small amount of seed . Goodidea, especially for expensive hybrid seed! J(pers. comm. Farmer Yousuf, Jessore, Bangladesh, 1998)Sometimes, the nursery is covered with a layer of mulch, e.g. rice straw or rice husk, to protect the soilfrom becoming very hot and drying out (during a warm and dry period) and to prevent weeds fromgerminating. It also prevents birds from roaming around in the beds and eating the seed. Usually, themulch has to be removed once the seedlings have germinated or it can be moved aside to give enoughspace to seedlings but still covering the area next to the seedlings. When straw is used as mulch, atleast the long pieces of straw should be removed. After germination, it is recommended to thin the plantsto 2-3 cm apart to ensure that each plant will have sufficient space and nutrients to become strong.When necessary, shade and shelter for heavy rainfall can be provided by placing polythene or bamboomats over the nursery beds. Do not shadow the nursery beds for too long a period as this results inweaker and stretched seedlings.3.7.2.2 Sowing in potsIn areas with heavy soil-borne disease infestation, or with unsuitable soil for a nursery site, it is possibleto raise seedlings in pots. Pots made out of banana leaf can be used, polybags, jars or other materials.The pots are usually removed at transplanting. The pots are usually filled with clean soil and somecompost. Various soil mixes can be tried, for example sub-soil with compost (see section 3.7.1.3).One or two seeds are sown in each pot. The pots are watered regularly and protected from full sun or rainif necessary.Cabbage Ecological Guide - 200040

Major Agronomic PracticesPotting seedlings versus flatfield beds, experiences from Asia:In a tomato study in Hai Phong Province, Vietnam, seedlings for the IPM treatmentswere raised in banana leaf pots filled with clean soil and compost, whereas farmerstraditionally raise them in flat field seed beds. Farmers found that there was less dampinngoffin seedlings, and less seed was needed, when plants were raised in clean conditionsin pots rather than in traditional seedbeds. J (pers. comm. Dr. J. Vos, 2000)Similar experiences are reported from Lao PDR, where cabbage seedlings raised inpolybags are found to recover quicker after transplanting and are ready for harvest about 7 to 10 daysearlier, compared to traditionally raised seedlings (pers. comm. A. Westendorp, 2000).Cabbage transplants are usually about 4 - 6 weeks old and have 4 or 5 true leaves when set into the field.Transplants usually have crooked stems; these should be planted up to the first leaves to ensure asturdy plant that will not fall over when full sized.Related exercises from CABI Bioscience/FAO manual:2-B.1. Farmers’ practices and problems during the nursery phase2-B.2. Design and testing of good nurseries2-B.3. Use of clean soil: subsoil versus topsoil2-B.4. Use of clean soil: solarization of the seed bed2-B.5. Use of clean soil: topsoil burning2-B.6. Use of clean soil: steam sterilization2-B.7. Broadcasting versus potting2-B.8. Fertilizing seed beds2-B.9. Roofing and screening of seed beds2-B.10. Mulching of seed beds2-B.11. Overhead or flood irrigation of seed beds2-B.12. Length of raising period2-B.13. Transplanting methods3.8 Field preparation3.8.1 Working the soilTillage or ploughing is carried out to prepare good plant beds.When turning the soil, insects that live or pupate in the soilmay come to the surface and are either dried out by the sunor may be eaten by birds. Ploughing can also control weedsand pests that remain in plant debris in the soil.Ploughing however, also disturbs the micro-organisms inthe soil and this may reduce soil fertility. To maintain andimprove soil fertility, it is important to apply organicmaterials such as compost every year.Ploughing may expose insects andpupae in the soil to predators like birdsand to the drying force of the sun.Sustainable soil practices are focussed on using less tillage and more organic materials, such as greenmanure or mulch, to increase biological activity in the soil. Less tillage is possible where enough mulchcovers the soil. See sections 3.5.3.4 and 3.8.4, and box below on conservation tillage.41 Cabbage Ecological Guide - 2000

Major Agronomic PracticesLeft-overs from a previous crop should be carefully removed and destroyed as it may still contain diseasesand pests which can spread into the new crop. These left-overs can be used for composting which, ifproperly done, will kill pathogens.When drainage of the field is problematic, or when crops are grown during the rainy season, it isrecommended to prepare raised beds for growing the crop and dig trenches between the beds for drainage.This is also a good practice when problems with soil-borne diseases can be expected: mostpathogens need water to spread and if there is an excess of water all the time, they can easily spread inthe field. Excess water in the soil, or even water-logging, results in weak plants which are more susceptibleto diseases and pests and give a lower yield.Conservation TillageIn conservation tillage, crops are grown with minimal cultivation of the soil. When the amount oftillage is reduced, the stubble or plant residues are not completely incorporated, and most or allremain on top of the soil rather than being plowed into the soil or removed. The new crop is plantedinto this stubble or small strips of tilled soil. Weeds are controlled with cover crops or herbicidesrather than by cultivation. Fertilizer and lime (if necessary) are either incorporated earlier in theproduction cycle or placed on top of the soil at planting. Because of this increased dependence onherbicides for weed control and to kill the previous crop, the inclusion of conservation tillage as a“sustainable” practice could be questioned. However, farmers and researchers are working on lessherbicide-dependent modifications of conservation tillage practices. In general, the greatest advantagesof reduced tillage are realized on soils prone to erosion and drought.(Peet, www4)Advantages• Crops use water more efficiently• Water-holding capacity of soil increases• Water losses from runoff and evaporationare reduced• Soil organic matter and population ofbeneficial micro-organisms aremaintained• Soil and nutrients are less likely to be lostfrom the field• Less time and labor is required to preparefield for plantingDisadvantages• Compaction of the soil may occur• Flooding or poor drainage may occur• Delays in planting when field is too wet ortoo cold• Carryover of diseases and pests in cropresidue• Transplanting in stubble is more difficultand may take longer resulting in delayedor less uniform crop maturity3.8.2 TransplantingCabbage transplants are usually about 4 - 6 weeks old and have 4 to 6 true leaveswhen set into the field. Thoroughly water plants 12 to 14 hours before transplantingto the field. Plants should be dug or cut loose from the soil when being transplanted;ensure the roots are not damaged and exposed to sun or drying wind.Some nurseries harden seedlings before they are sold for transplanting. Seedlingsare hardened by withholding water and nutrients for a certain period of time. Thisresults in seedlings that can survive adverse conditions and are therefore more likelyto recover quickly from the transplanting “shock”.Cabbage Ecological Guide - 200042

Major Agronomic PracticesTransplanting should preferably be done in the late afternoon or evening. Transplants usually have crookedstems; these should be planted up to the first leaves to ensure a sturdy plant that will not fall over whenfull sized. Irrigate frequently after transplanting during dry periods. Transplants are very sensitive to waterstress.Removing lower leaves at transplanting: a Lao experienceDuring a Farmer Field School on cabbage in Ban Thanaleng, Lao PDR, farmers studied the effect ofremoval of two lower leaves at the time of transplanting. The farmers found that transplants with 2lower leaves removed recovered 1 to 2 days quicker than seedlings transplanted withall leaves. In India and Bangladesh, this is a common practice in eggplant, to limitevaporation and to shorten the recovery phase of the seedling after transplanting.(IPM Cabbage FFS Ban Thanaleng, Lao PDR, Nov 1997 – Feb. 1998)3.8.3 Planting densityPlanting density has an effect on crop production and susceptibility to diseases. The wider the density,the more area one plant has to grow and the more nutrients are available to the plant. More space andnutrients usually result in larger plants with bigger heads. This can be both an advantage and a disadvantage,depending on market requirements. Despite the larger head size, the overall production of an areawith a low planting density may still be low because there are less plants.Planting density also has an effect on the climate within the crop. In a close planting, wind and sunshinecannot reach to the soil level and as a result, the lower leaves of the crop stay wet longer. This canstimulate disease infection because many diseases need water to infect the plant. When serious problemsare present with a pathogen, for example leaf spot, an option would be to plant at a wider spacing. Thiswill keep the plant dryer and this prevents spores (the ‘seed’ of a fungus) from germinating and infectingthe plant.In addition, pest insects such as armyworm caterpillars (Spodoptera sp.) can easily walk from one plantto the next when leaves of adjacent plants touch.Adjusted spacing to meet market requirements : a Philippine experienceIn some areas in the Philippines, farmers plant their cabbages closer than the “official” 45 x 45 cm. Thisresults in a smaller head size which is in demand in market and sells at higher prices than large heads.close plantingwider spacing:small heads larger headsSome factors related to spacing are listed in the table below.Table 3.8.3 : Some factors related to plant spacingNarrow spacingWide spacingmore plants per area = higher initial costs fewer plants per area = lower initial costssmall plantslarger plantsmore, but smaller size, headsfewer, but larger size headsmight increase disease incidencemight reduce disease incidence43 Cabbage Ecological Guide - 2000

Major Agronomic Practices3.8.4 MulchingMulching means keeping the soil surface covered with non-transparent material. Mulching reduces weedgermination and it will keep the soil cool and moist because the sun cannot shine directly on the soil.Organic mulch can provide shelter for predators such as ground beetles and spiders. Mulching can bedone both on the nursery after sowing (also to prevent birds from eating the seed) and after transplantingin the main field. Mulch on the nursery usually needs to be removed once the first seedlings havegerminated.Mulch can be a layer of organic material, for example rice straw or a layer of green leaves, saw dust oreven pulled out weeds without seed. Mulching can also be done with non-transparent plastic sheets.This is however, quite expensive! Sheets should be non-transparent because that prevents germination ofweeds. Seed usually need light for germination. A disadvantage of using black (or non-transparent)plastic sheets can be that the soil temperature is increased. This type of mulch should be removed whentemperature becomes excessive (over 32 o C) under the covers.In cool areas, a rise in soil temperature may be an advantage as it increases root growth and may induceearly yields, and in some cases increase total yields.Mulching may have a role in reducing pests and diseases. Plastic mulches with aluminium film havebeen shown to reduce aphid attacks. The shiny aluminium reflects light and deters aphids. Silver coloredplastic has the same effect, white and yellow plastics to a lesser extend. This is particularly useful whereaphids transmit virus diseases, such as in tomato, or chili. It is probably not economical for use incabbage.Diseases that spread with soil particles with splashing water from rain, such as black rot (Xanthomonascampestris), and leaf spot (Alternaria brassicae) cannot spread so easily when the soil surface is coveredwith a mulch.See also section 3.5.3.4 on organic mulch.Related exercises from CABI Bioscience/FAO manual:2-C.1. Farmers’ field preparations and problems2-C.2. Plant spacing2-C.7. Mulching of plant beds: organic and inorganic mulchesCabbage Ecological Guide - 200044

Major Agronomic Practices3.9 Water management3.9.1 DrainageThe most important water management practice is providing drainage to keep soil around roots frombecoming waterlogged. This is especially important when cabbage (or other vegetables) is rotated withpaddy rice, which is usually grown on clay soils that are difficult to drain and stay wet for longer periodsof time. Seed and seedlings are likely to rot in wet soil. When soil remains wet and muddy during therainy season, the plants will grow slower and head formation may be hampered. Some diseases caneasily spread with the ground water and attack a weakened plant. When the soil tends to stay too wet,dig some trenches to help dewatering. Growing the plants on raised beds and/or plastic covered bedsmay also help to keep the soil moisture down.Wet soil and diseases….When the nursery soil stays wet for a long period, certain soil fungi can cause damping-off diseaseof the seedlings, and they can even cause death of the small roots emerging from the seed. Soseedlings never even emerge above the soil…When seedlings are grown in wet soil for a long time, they are weakened and more susceptible todiseases. And the fungi causing damping-off can grow and spread easily in wet soil… L3.9.2 IrrigationProper irrigation can be critical for maintaining high yields and quality. Soils with adequate organic matterusually have a large water absorption capacity and do not need frequent irrigation. Soil type does notaffect the total amount of water needed, but it does influence frequency of water application. Lighter soilsneed more frequent water applications, but less water applied per application. Sandy soils may requirewater at more frequent intervals as water drains off quicker.Where irrigation facilities exist, there are sometimes opportunities for manipulating pests. Where the soilis leveled, it is in some cases possible to flood the field with water or to dry the soil out to control pestsand weeds. Some pest insects that survive in the soil like cutworms and nematodes and some weedscan be drowned by putting the field under water. Obviously, this is done before transplanting the crop. Thefield has to be under water for about 4 weeks and will need some time to dry up properly before a newcrop is planted. This method does not control all soil-borne diseases!Flooding the field by rotation with paddy riceIn Indonesia, chili grown in rotation with paddy rice had less problems with soil-borne diseases andnematodes than chili grown in unflooded fields. During the rice production, the field is flooded andnematodes and other pathogens in the soil are killed. See section 3.12 on crop rotation (Vos, 1994).The irrigation method may also have consequences for the insect and disease populations. There areexamples of effective diamondback moth reduction by using overhead sprinkler irrigation during dusk J.The irrigation disrupted the mating and oviposition of the adults.However, overhead irrigation can increase diseases. The spores of leafspot in cabbage for example, caneasily germinate when the leaves are wet L.45 Cabbage Ecological Guide - 2000

Major Agronomic PracticesThe use of ditch and furrow irrigation is usually preferred to overhead irrigation. Ditches also ensure rapiddrainage of excess soil moisture during the rainy season.Other useful water management practices to help keeping foliage dry to prevent spread of water-bornepathogens include:lllllplanting in wide rows to increase air flow between rows.orienting rows towards prevailing wind.planting with wide spacing in the rows.irrigating early enough to give plants a chance to dry during the day.working with plants only when leaves are dry.Related exercises from CABI Bioscience/FAO manual:2-C.8. Flooding and overhead irrigation3.10 Intercropping and trap crops3.10.1 Intercropping and barrier cropsIntercropping is the simultaneous cultivation of two or more crops in one field. It can also be called mixedcropping or polyculture. When plants of different families are planted together it is more difficult for insectpests and diseases to spread from one plant to the next. Insects have more difficulty in finding hostplants when they are camouflaged between other plants. Fungus spores may land on non-host plantswhere they are lost. Natural enemies of insect pests get a chance to hide in the other crop. When theintercrop is taller than the cabbage plants they can form a “barrier” thus reducing spread of insect pestsand diseases.Certain intercropped plants excrete chemicals or odors which repel insect pests of other plants. Examplesare onion and garlic. The strong smell repels some insects, and they fly away and will not attack otherplants growing between the onion or garlic plants. Intercropped cabbage with tomatoes is reported toreduce diamondback moth (Plutella xylostella) infestation. See box below.Intercropping for diamondback moth control?In both Indonesia and Malaysia, it was found that the population ofdiamondback moth (DBM) on cabbage was less in cabbage-tomatointercropped plantings than in fields with cabbage alone. Also, parasitism ratesof DBM larvae were higher in the intercropped field. JSimilar results were found in Sri Lanka but in Singapore it didn’t work so well. (In: Sivanaser, 1991).Because the results vary from location to location it might be worth trying if this cropping systemwould be practically useful in your area. See box below.Other plants may have nematicidal activity, killing nematodes in the soil. An example is sesame: rootextracts caused mortality of nematodes in laboratory tests . Another “famous” nematode-killer is theflower Tagetes sp. which can be effectively controlling nematodes on tomato (Tumwine, 1999).Intercrops could also reduce the risk of crop failure by providing an alternative crop and additional incometo a farmer.Cabbage Ecological Guide - 200046

Major Agronomic PracticesHowever, when the intercrop is taller than cabbage, or grown very close to the cabbage plants, it maycause yield reduction due to competition for light, space and nutrients. Other disadvantages includemore difficult harvesting operations due to different ripening times of the crops, and the planning of croprotation schedule is more complicated. Intercropping is usually a bit more labor intensive.How to try intercropping in your field:Take a small portion of your field, for example a few square meters and plant both cabbage andtomato, a few rows of each. The remaining part of the field is planted with cabbage. Monitor a fewplants weekly for the numbers of pest insectsand the incidence of diseases. Check ifthere is less infestation of diamondbackmoth (Plutella xylostella) and other insectpests or diseases in the intercropped areaas compared to the portion of the fieldin which only cabbage is grown. Trydifferent crops for intercropping, forexample cabbage-onion, tomatoonion.3.10.2 Trap cropsA trap crop is a crop other than cabbage that attracts insect pests so that these pests will not harm thecabbages. Usually, trap crops are also members of the cruciferous family because they have to attractthe same insects that will attack cabbage. Some people find this is a disadvantage of planting trap cropsbecause pests are attracted to the field…..!The trap crop should be sown thickly all around the area where crucifers will be grown, at least 10 daysbefore the cabbage is transplanted. The idea is that the trap crop is established in the field earlier thanthe cabbage so that pests will attack the trap crop first. Then the infested trap crop can be destroyed butit can also be treated with pesticides, or left in the field. The advantage of leaving the trap crop may bethat the infested trap crop attracts natural enemies that will be present when the cabbage plants will beattacked by pests. When pesticides are used on the trap crop, there is a risk that (especially) diamondbackmoth builds up resistance against pesticides faster than without treatment.Several studies report that (Indian) mustard is an effective trap crop because it reduces numbers of pestinsects, and in some cases, improves yield of the main crop.For example, field studies in India showed that diamondbackmoth (Plutella xylostella), cabbage heart caterpillar(Crocidolomia binotalis), and aphids (Brevicorynebrassicae) preferred mustard to cabbage when thechoice was available. The ideal crop combinationin this study was 9 rows of cabbage followedby 1 paired row of mustard. In one of theserows mustard should be sown15 days before cabbage, andin the other row, mustardshould be sown 25 days aftercabbage (Srinivasan, 1991).47 Cabbage Ecological Guide - 2000

Major Agronomic PracticesRelated exercises from CABI Bioscience/FAO manual:2-C.3. Mixed cropping versus monocropping3.11 Harvest and post-harvestHeads should be firm-to-hard at harvest, but delaying harvest may increase the riskof splitting mature heads if soil moisture increases suddenly. Heads are cut at thebase and the outer leaves are trimmed off. For the fresh market, fields may be cut3 to 5 times. When hybrid varieties are used, a higher percentage of the plants canbe harvested at one time.Heads must be cooled immediately after harvest. Cabbage can be stored at 0- 2 o C and 95% relative humidity for 3 to 6 weeks (early crop) or 5 to 6 months(late crop). Storage life can be prolonged even further at low O 2(2%) and highCO 2(5%) and with controlled atmosphere storage systems, where available.Bacterial soft rot is the main problem in storage.Related exercises from CABI Bioscience/FAO manual:2-C.10. Assessment of harvest time2-C.11. Harvesting practices and crop residue management3.12 Crop rotationCrop rotation is necessary to:1. Avoid build up of large populations of certain pest insects and pathogens.Some of the more common serious pests and diseases which live in the soil attack a range of plantswithin the same botanical family - but no others. If the sorts of plants they attack are continually grownin the soil, the pest and diseases can build up to serious populations. Once a soil-borne disease hasentered a field it is very difficult to get rid off. If there is a break of several seasons or even several yearsin which other crops (of a different crop family) are grown, their numbers will diminish and they willeventually disappear. This is the main reason for rotating crops.2. Avoid nutrient deficiency and degradation of soil fertility.Another reason for crop rotation is that it reduces fertility degradation and nutrient deficiency. When thesame crop is planted in the same field every season, there will be a continuous consumption of the samenutrients from the soil. Adding chemical fertilizers will supply only part of the nutrients that are consumed,mostly N, P and K. Adding chemical fertilizers containing the deficient nutrients will not solve the problem.It is necessary to introduce crop rotation and supply organic matter to the soil. Rotating with greenmanure crop (see section 3.5.3.2) and adding legumes (supplying nitrogen) to the rotation schedule istherefore recommended.Nutrient consumption is quite different for each crop. In general however, nutrient consumption can beranked from low to high consumption:1. legumes2. root crops (e.g. carrot, radish)3. leaf crops (e.g. cabbage, lettuce)4. fruit crops (e.g. tomato, cucumber)5. cereals (e.g. rice, barley)Cabbage Ecological Guide - 200048

Major Agronomic PracticesSome examples of main crop families:CrucifersSolanaceousLegumesOnionsCucurbitscabbage, Chinese cabbage, radish, cauliflower, pak choi, broccoli, turnip,mustard, rapetomato, potato, pepper, chili, eggplantall types of beans, all types of pea, groundnut, alfalfa, cloversonion, garlic, shallot, leekcucumber, gourds, luffa, melons, pumpkins, courgetteRotation is most effective against diseases that attack only one crop. However, controlling the manydiseases that infect several crops in the same plant family requires rotation to an entirely different family.Unfortunately some pathogens, such as those causing wilts and root rots, attack many families androtation is unlikely to reduce disease.In addition, some fungi produce resistant, long-lived reproductive structures as well as the immediatelyinfectious forms. For example, the black sclerotia produced by the fungus Sclerotinia can survive foryears. Pythium and Phytophthora can also produce long-lived resting spores. Such spores help thesefungi to survive during a long time without a host. How long such pathogens can survive without a hostplant depends on factors like environment, temperature, ground water, etc. Some indications on “survivalrates” per disease are mentioned in the sections on individual diseases. A few examples:Disease Can stay alive in soil without cabbage plant for ..Black rot 1- 2 yearsBlack leg 2 -3 yearsClubroot 7 - 20 yearsNext to this, you can set up a small study as described below to check if soil-borne pathogens like blackleg, are still present in a field.How to check for soil-borne cabbage pathogens in a field:Plant a non-cruciferous crop in yourfield but leave about 2 or 3 small areaswithin the field which you plant withcabbages. These are your test areas.Check at regular intervals whether anysoil-borne diseases occur in the testareas. When you find a disease, youknow it is still there and you will haveto wait at least one more seasonbefore planting cabbages or anothercruciferous crop again. Check if theresmall area planted with cabbagestill are old cabbage leaves in theneighborhood of your field or in the soilwhich can be the source of infection. These should be removed and destroyed.rowsanothercropWhen no disease occurs you can try planting cabbages again in the whole field next season.GIt should be stressed that this test is not 100% proof! Soil-borne diseases are often patchy and asuccessful test may not give a 100% guarantee that there are no soil-borne diseases. The more testareas you try, the more chance there is to “hit” a soil-borne disease.Related exercises from CABI Bioscience/FAO manual:2-A.1. Importance of crop rotation49 Cabbage Ecological Guide - 2000

Ecology of Insect Pests and Natural Enemies4ECOLOGY OF INSECT PESTS ANDNATURAL ENEMIESSUMMARYInsect ecology studies insects in their environment. The environment (e.g. climate,food sources, natural enemies) determines whether an insect population becomesa pest or not.Insects can damage plants by eating leaves, by sucking plant juices, or byfeeding inside the leaves. However, not all insect feeding reduces yield! Cabbageplants can compensate for feeding injury because more leaves and roots areproduced than actually needed for head formation. So, not all “pests” are “pests”!Actually, some insects are needed to keep the natural enemy population alive. Bysetting up insect zoos, the functions and life cycles of insects and natural enemiescan be studied.Natural enemies (predators, parasitoids, pathogens and nematodes) reduce pestinsect populations. They can be indigenous or reared and released into the field.The latter is becoming more and more important for many vegetable insect pests.A number of management and control practices for insect pests are described.Cabbage Ecological Guide - 200050

Ecology of Insect Pests and Natural Enemies4.1 IntroductionEcology is the study of interrelationships between organisms and their environment. The environment ofan insect consists of physical factors such as temperature, wind, humidity, light and biological factorssuch as other members of the species, food sources, natural enemies and competitors (organismsusing the same space or food sources).temperatureother membersof the specieswindÛhumiditylightcompetitorsfood sourcesnatural enemiesInsect ecology: the interrelationships between insect and environmentThese interrelationships are a reason that insect pest species cannot in all circumstances grow to largepopulations and damage crops. There may be large numbers of predators that eat the pest insects. Theweather conditions may be unfavorable for a quick life cycle because insects usually like warm, dryweather. The plant variety may not be very attractive for the pest insects to eat. And there may be manymore reasons.In Agro-Ecosystem analysis, insects are considered as populations rather than individuals. One singleinsect that eats a cabbage leaf will never cause yield loss in a large field but a population of ten thousandleaf-eating caterpillars may do.Learning to recognize natural enemies and understanding how they work, and how their impact can bequantified, is very important in pest management. Natural enemies do nothing but reduce pest populations,that is why they are called the “Friends of the farmer”! The work of natural enemies can reduce the needfor pesticides. This saves money and time, and possibly the environment and human health. JIn many areas, the use of pesticides is still a common practice for insect and disease control. Mostpesticide sprays are very toxic to natural enemies. The death of natural enemies means that insect pestspecies can increase in number very rapidly. Normally, natural enemies will remove a large number of thepest insects but when there are no natural enemies, the pest insect population can grow rapidly. Especiallywhen there is a lot of food available, like in large fields grown with the same crop, or in areas with manysmaller fields grown with the same crop. When the pest insect population is very large, more insecticideswill be used. Life cycles of natural enemies generally take longer periods of time to complete than thoseof pest insects. Once insecticides are being used in the ecosystem, it is difficult to bring back the naturalenemies within one season. Insecticides should be used only when there are no other options for controland there is a definite and visible need. This is one of the important reasons to monitor fields regularly.(modified from Hoffmann et al, 1993; and Weeden et al, www12)51 Cabbage Ecological Guide - 2000

Ecology of Insect Pests and Natural Enemies4.2 Insect anatomyInsects have three body regions: head, thorax, and abdomen. The head functions mainly for food andsensory intake and information processing. Insect mouthparts have evolved for chewing (beetles,caterpillars), piercing-sucking (aphids, bugs), sponging (flies), siphoning (moths), rasping-sucking (thrips),cutting-sponging (biting flies), and chewing-lapping (wasps). The thorax provides structural support forthe legs (three pairs) and, if present, for one or two pairs of wings. The legs may be adapted for running,grasping, digging, or swimming. The abdomen functions in digestion and reproduction.Insects haveThree body regionsSix legsOne or two pair of wingsOne pair of antennaeAs simple as it may seem,knowing what type of mouthpartsan insect has can be importantin deciding on a managementtactic. For example, insects withchewing mouthparts can beselectively controlled by someinsecticides that are applieddirectly to plant surfaces and areonly effective if ingested; contactalone will not result in death ofthe insect. Consequently, naturalenemies that feed on otherinsects, but not the crop plant,will not be harmed.Chewing insectsPiercing and suckingCabbage Ecological Guide - 200052

Ecology of Insect Pests and Natural Enemies4.3 Insect Life CyclesInsect life cycles can be complete or incomplete(gradual). In complete life cycles, or better: lifecycles with a complete metamorphosis, insectspass through the egg, larval, pupal and adultstage. A larva is a young insect that looks verydifferent from the adult. Larvae may also behavedifferently from the adults. There are generallyseveral larval stages (also called instars). Eachlarval stage is a bit larger than the previousstage, requiring a molting or shed of the outerskin between the stages.Complete life cycles can be found with moths,butterflies, beetles, flies and wasps.Complete metamorphosis : lady beetle : egg,4 larval stages, pupa, adult(from : Hoffmann, 1993)In incomplete life cycles, or better: life cycles with anincomplete metamorphosis, insects go through egg,nymph and adult stage. There are generally severalnymphal stages. A nymph is a young insect thatresembles the adult except that they lack wings andthe nymph may be colored differently than the adult.No pupal stage is present. Nymphs and adults usuallyhave similar habitats and have similar hosts. Eachnymphal stage is a bit larger than the previous stageand requires a molting or shed of the outer skin betweenthe stages. Incomplete life cycles can be foundwith bugs, grasshoppers and aphids.Incomplete metamorphosis : aflower bug : egg, 5 nymphalstages, adult(from Hoffmann, 1993)Insects’ growth rate dependents on the temperature oftheir environment. Generally, cooler temperatures resultin slower growth; higher temperatures speed up thegrowth process. If a season is hot, more generationsof an insect may occur than during a cool season.Every insect species will have its own optimum temperature for development. Some insects can live andreproduce only at lower temperatures whereas others need high temperatures. That is why you will oftenfind other insect species in the tropics than in temperate regions. This also applies for plant pathogens.Understanding how insects grow and develop will contribute to their management. Some insects areactive predators or parasitoids during only one specific stage of their life. The hoverfly larvae, for example,are voracious predators but the adults only feed on nectar from flowers. Other insects are susceptible tocertain biological or chemical insecticides during one specific stage of their life or none at all. Larvae ofleafminers for example, are only found inside plant tissue. Spraying contact insecticides (unfortunately afrequent practice) is simply a waste of money because leafminers will not be affected. Understandinginsect life cycles helps making sensible crop management decisions regarding pesticide use.53 Cabbage Ecological Guide - 2000

Ecology of Insect Pests and Natural EnemiesInsect Zoo: studying life cycles of insectsTo study different stages of a life cycle of insects, try rearing the insects in an insect zoo. Althoughit may not be easy to study a full life cycle, it is possible to study some stages, for example thestages that cause plant damage. Collect some insects or eggs, pupae orlarvae/nymphs from the field and put them in a glass or plastic jar with somefresh leaves from an unsprayed field. When studying life cycles of predators,feed them with the appropriate prey. Put some tissue paper in the jar to avoidcondensation.Close the jars with fine netting that permits air circulationand keep them in the shade.Insect zoos are also suitable to find out what insects(larvae/nymphs to adults) are emerging from eggmasses, and to rear larvae or pupae that you find in thefield but don’t know what species they are.Related exercises from CABI Bioscience/FAO manual:4.1 Insect zoo4.A.1. Life cycle of caterpillar pests4.4 How can an insect damage a plant?A plant needs its leaves to absorb sunlight to make sugars for energy andgrowth (this process is called photosynthesis). The sugars are transportedthrough the veins of the plant to other parts like roots and stems.When an insect feeds on the leaves and reduces the leaf area, like somecaterpillars do, less sugar is produced and the plant has less energy forgrowth and development.When insects are sucking on the leaves of the plant, like aphids do, they are sucking the sugars out ofthe plant cells or the veins. This leaves less sugar available for the plant for its growth and development.In additions, some insects excrete sugary wastes (honeydew) on which fungi can grow. Leaves becomeblack with these fungi and as a result, photosynthesis is reduced.Other insects like leafminers feed inside the leaf and destroy part ofthe veins, resulting in less sugar transport. Less sugar available forplants means less plant growth and reduced plant health, and thatmay eventually lead to an overall lower yield.It is important to note that not all insect feeding reduces yield!See section on compensation below.A special case are insects that can transmit virus diseases. Thesehoneydewinsects are usually sucking insects like aphids, jassids, thrips andwhitefly. A virus infected plant has virus parts in most cells andsometimes inside veins. When an insect feeds on an infected plant, it will suck with the plant juice alsosome virus particles. These particles either stick to the mouth parts of the insect or they are swallowedinto the stomach of the insect. When the insect starts feeding on a fresh plant, the virus particles aretransmitted from the mouth parts or stomach into the new plant. This plant then becomes infected too.Cabbage Ecological Guide - 200054

Ecology of Insect Pests and Natural EnemiesThere are some virus diseases known in cruciferous crops, however, in most areas in South East Asia,they are considered to be of minor importance and will therefore not be discussed in this guide.4.5 Plant compensationNot all insect feeding reduces yield. The cabbage plant is able to compensate for feeding because moreleaves and roots are produced than actually needed for head formation. Some studies even show thatyoung cabbage plants that loose the main bud (growing point) compensate for that loss by producingother shoots and when all shoots are removed but one, a normal head can develop! Studies in Vietnamfor example, showed that when the growing point of cabbage plants were removed up to 14 days aftertransplanting, the cabbage yield was still 75% of the plants were the growing point was not removed.When the growing point was removed later, up to 35 days after transplanting, the cabbage yield droppedto 55% (FAO - TOT report Vietnam, 1995)þ Plants beyond the four to five true leaf stage can tolerate up to fiftypercent defoliation until the prehead stage without yield loss.For example, studies done in Vietnam showed that cabbage plants that weredefoliated up to 50% at 7, 14, 21 and 28 days after transplanting, still gave morethan 90% yield compared to the undefoliated plants (FAO - TOT report Vietnam,1995).Low levels of insect feeding and minor disease infections do not significantly reduce yields. It is alsoimportant to remember that spraying for insects that are not causing yield loss is a waste of money andtime and it may cause needless environmental pollution.Related exercises from CABI Bioscience/FAO manual:4.A.2. Diamondback moth injury symptoms on cabbage4.A.3. Plant compensation study4.6 A pest or not a pest insect… : how to find out !Many insects can be found in a cabbage field. Not all of them can be called “pests”, in fact, very fewinsects have the potential to cause yield loss to cabbage. The few insects that do cause some yield lossin some fields in some seasons, are called “pest insects”. As the pest insects do not cause yield loss inall fields all the time, a better term to use would be“herbivores”. Herbivores do not just eat plants or suckthe plant juices, they have an additional function: theyserve as food or as a host for natural enemies.There are many potential “pest insects” that do notbuild up in populations large enough to causeeconomic yield loss. They may chew a few leaveshere and there but this does not affect the yield orquality of the cabbage. In fact, their presence keepsthe population of natural enemies alive so one couldalmost say at that time they are “beneficial”....!55 Cabbage Ecological Guide - 2000

Ecology of Insect Pests and Natural EnemiesThe goal of growing cabbage is to produce as much yield as possible without spending a lot ofmoney. If there are no pests to control, do not waste money on pesticides that can damage thenatural enemy population.When you find insects in the field, it is sometimes difficult to judge whether they are actually damagingthe plants or not. Some insects may just be crop visitors passing by and resting on the plants or on thesoil, or neutrals that live in the crop but do not eat from the plants nor influence the pest populations asnatural enemies directly. Neutrals can be a food source for natural enemies.If you find insects and you are not sure what they are: pests, natural enemies, or crop visitors/neutrals,set up an insect zoo to find out what the function of that insect is. See box below.Insect Zoo: check functions of insectsTo set up an insect zoo, take a few glass/plastic jars, or plastic bags, put in some fresh leaves orfrom an unsprayed field together with the insect. Close the jar with fine netting that permits aircirculation and keep it in the shade. Monitor if the insectstarts feeding on the leaves in the next hours, up to 2days. If that insect did not eat the leaves, it may not bea pest insect. (don’t keep the insect inside for morethan 3 days when it does not eat: remember that whena person is locked in a room with nothing but a book,he may get so hungry after a few days that he will startchewing the book....: that does not prove that humanseat books....!).Similarly, to find out if the insect is a predator, put it ina jar and give it some prey (aphids or small diamondbackmoth larvae) with some leaves. Observe if it feeds on the prey in the next hours up to about 2days. Similarly you can test if predators eat neutrals.When you find that an insect is eating the cabbage leaves, it could be classified as a “pest insect”. Butagain, as explained above, not all plant damage results in yield loss. Thus, not all “pest insects” areactually “pests”!Whether or not a pest insect is a pest depends not only on the population of that insect but also on thegrowth stage of the crop in which it occurs. For example, most caterpillars can severely damage cabbageplants when they feed on young seedlings. When they destroy the growing points, this may result inmultiple heading (check section 4.5 on plant compensation!). Also caterpillar feeding during the headingstage is unfavorable as it may result in damaged heads which fetch a lower price in the market. Butsimilarly, when flea beetles eat holes in the leaves when the plants are already quite large, it does notinfluence the yield or quality of the cabbages.Related exercises from CABI Bioscience/FAO manual:1.6. Show effects of beneficials incl. natural enemies4.1. Insect zoo4-A.4. Assessment of impact of ground-dwelling predators4-A.5. Measuring the parasitism level of caterpillarsCabbage Ecological Guide - 200056

Ecology of Insect Pests and Natural Enemies4.7 The Friends of the FarmerNatural enemies are the friends of the farmer because theyhelp the farmer to control insect pests (herbivores) on cabbageplants. Natural enemies are also called beneficials, or biocontrolagents, and in case of fungi, antagonists. In countries like Bangladesh,natural enemies are called crop defenders.Most natural enemies are specific to a pest insect. Some insectpests are more effectively controlled by natural enemies than others.Natural enemies of insect pests can be divided into a few largergroups: predators, parasitoids, pathogens, and nematodes. Nematodes are oftenlumped together with pathogens. Some of the main characteristics of naturalenemies of insect pests are listed below. The major natural enemies of cabbageinsect pests are described in more details in chapter 6. Antagonists, naturalenemies of plant diseases, are described in section 7.10.CHARACTERISTICS OF NATURAL ENEMIES OF INSECT PESTS:Predators· Common predators are spiders, lady beetles, ground beetles, and syrphid flies.· Predators usually hunt or set traps to catch a prey to feed on.· Predators can feed on many different species of insects.· Both adults and larvae/nymphs can be predators.· Predators follow the insect population by laying more eggs when there is more preyavailable.Parasitoids· Parasitoids of cabbage pests are commonly wasps or flies.· Attack only one insect species or a few closely related species.· Only the larvae are parasitic. One or more parasitoid larvae develop on or inside asingle insect host.· Parasitoids are often smaller than their host.Pathogens· Insect-pathogens are fungi, bacteria or viruses that can infect and kill insects.· Pathogens require specific conditions (e.g. high humidity, low sunlight) to infect insectsand to multiply.· Most insect-pathogens are specific to certain insects groups, or even certain lifestages of an insect.· Commonly used insect-pathogens are Bacillus thuringiensis (Bt), and NPV virus.Nematodes· Nematodes are very little worms.· Some nematodes attack plants (e.g. rootknot nematode). Others, calledentomopathogenic nematodes, attack and kill insects.· Entomopathogenic nematodes are usually only effective against pest in the soil, orin humid conditions.Natural enemies of insect pests do not damage plantsand they are harmless to people!57 Cabbage Ecological Guide - 2000

Ecology of Insect Pests and Natural Enemies4.8 Natural enemy efficiencyA successful natural enemy should· have a high reproductive rate: so that populations of the natural enemy can rapidly increase whenhosts are available,· have good searching ability,· have host specificity,· be adapted to different environmental conditions, and· occur at the same time as its host (the pest).It is probably impossible for any one natural enemy to have all these attributes, but those with several ofthem will be more important in keeping pest populations low.Efficiency of predators, in addition, is determined by their appetite. For example, ladybeetle adults mayeat as much as 50 aphids per day. To check the appetite of predators, the following experiment is easyto do.The Predator Appetite Test…!Catch a predator, e.g. a ladybeetle or a syrphid larva, and place it carefully in a jar,together with some fresh leaves and a paper tissue to avoid condensation of water.Put a leaf with a known number of prey in the jar, e.g. 20 aphids.Take another jar and place a leaf with the same number of aphids inside, but withoutthe spider or ladybeetle. This is the control, to see how quickly a group of 20 aphids can multiply.After 2 or 3 days, count the number of aphids alive in both jars. Discuss if the predator has eaten theprey and how effective it will be in field situations.Appetite is one factor to determine effectiveness. Ladybeetles, for example, are effective predators whenpest populations are high. They are thought to be less effective at lower pest densities.In case of parasitoids, the number of adults emerging from one host (the pest insect) can be an importantfactor to determine efficiency. Many adults emerging from a pest insect can each again parasitize a newhost. This way parasitoid population builds up more rapid than when only one adult emerges from a host.Related exercises from CABI Bioscience/FAO manual:4-D.1. Predation on sucking insects in insect zoo4-D.2. Cage exclusion of natural enemies in the field4.7. Direct observations of consumption rates of predators in the field4.5. Studying predators in the field.4-A.5. Measuring the parasitism level of caterpillars4-A.6. Parasitisation on diamondback moth of cabbage4-A.7. Effect of parasitisation on feeding behavior of diamondback moth4-A.17. Life cycle and biology of the parasite Diadegma semiclausum4-A.18. Life cycle and biology of the parasite Cotesia plutellae4-A.19. Life cycle and biology of the parasite Diadromus collaris4-A.20. Life cycle and biology of the parasite Cotesia glomerata4-A.21. Preference of host stages by Diadegma semiclausum (or Cotesia plutellae)Cabbage Ecological Guide - 200058

Ecology of Insect Pests and Natural Enemies4.9 Managing natural enemiesJust like the crop and pest insects are managed, natural enemies also must be managed. There aremanagement practices that kill pests but also kill natural enemies. It is obvious that management practicesfor natural enemies should be focused on preserving them and as much as possible increasing theirnumbers. Indigenous natural enemies are adapted to the local environment and to the target pest, andtheir conservation is generally simple and cost-effective. Natural enemies that are introduced from outside(for example those that are reared in insectaries and released into the field), often require a different wayof augmentation. Conservation methods are often similar.Some tactics for conservation and augmentation of natural enemies:1. Allow some insect pests in the field: these will serve as food or as a host for natural enemies.Cabbage plants can compensate for quite some injury and not all insect feeding results in yieldloss. Monitor the field regularly!2. Be extremely careful with using pesticides: most pesticides (even several fungicides!) are toxic tonatural enemies. Even pesticides that claim to be very selective and harmless to natural enemiesmay still cause problems. You can test this yourself! See box below.Effects of pesticides on natural enemies: a study example1. Prepare hand sprayers with the pesticide to be tested.2. Select a few plants in the field. Label plants with name of treatment and spray them with thepesticide. Let leaves dry on the plant.3. Pick one or several leaves from each labeled plant and place these in jars (use gloves!).4. Collect predators, e.g. spiders or lady beetles from the field (use a small brush).5. Place predators in the jars, close the lid and place a piece of tissue paper between the lid andthe jar to avoid condensation inside.6. Check condition of predators after 8 and 24 hours.Instead of leaves, a piece of cloth can be sprayed with pesticides. Rest of study as above.Note: When handling pesticides wear protective clothing and wash with plenty of soap and waterafterwards.3. Do not use insecticides before there is a serious infestation of a pest insect. Don’t apply “just incase” or “because my neighbor is also spraying”. This is not only a waste of money but mayactually result in MORE problems with pest insects because they can increase their populationquickly when there are no natural enemies around.4. If an insecticide is needed, try to use a selective material in a selective manner or very localized,on infested plants only.5. When the borders of the field are covered with weeds, especially when they are flowering weeds,these borders can provide a shelter for natural enemies. Mixed plantings can have a similar effect.Adult natural enemies (e.g. hoverflies, Diadegma sp.) may also be attracted to flowers for feedingon the nectar inside the flowers. Many adult parasitoids live longer, and are therefore more effective,when there are sufficient flowers to feed on. Such practices are easily incorporated into homegardens and small-scale commercial plantings, but are more difficult to accommodate in largescalecrop production. There may also be some conflict with pest control for the large producerbecause of the difficulty of targeting the pest species and the use of refuges by the pest insects aswell as natural enemies.59 Cabbage Ecological Guide - 2000

Ecology of Insect Pests and Natural Enemies6. Many adult parasitoids and predators also benefit from the protection provided by refuges such ashedgerows and cover crops. Other shelters may be provided for natural enemies to survive. Anexample is given in the box below.Manipulation of Natural Enemies in rice straw bundlesSome of the predators present in rice fields are alsopresent in vegetables. Spiders and other predatorsseek refuge in rice straw bundles at the time of riceharvest. If these straw bundles or tents are placed inrice fields when the crop is harvested and naturalenemies are allowed to colonize them, the bundlesmay be moved to vegetable plots where predatorscould colonize vegetables more quickly. Thus,conservation/augmentation of natural enemiesthrough manipulation of straw bundles could be usefulin reducing the impact of vegetable insect pests.Related exercises from CABI Bioscience/FAO manual:4.9. and 4.10. Importance of flowers as food source to adult parasites.4.10 Purchase and Release of Natural EnemiesIn several countries in Asia, commercial or non-commercial insectaries rearand market a variety of natural enemies including several species of parasitoids,predaceous mites, lady beetles, lacewings, praying mantis, and pathogenssuch as NPV (virus), and Trichoderma. Availability of (commercially) availablenatural enemies in a country also depends on the regulations of this countryregarding registration (Regulatory Affairs).Numerous examples from Asia exist on the use of reared natural enemies for release in the field. Someof those include the release and establishment of the parasitoid Diadegma semiclausum for control ofdiamondback moth in highland cabbage in various Asian countries. Other examples are the introductionof the parasitoid wasp Diadromus for diamondback moth control in Vietnam. Introduction of naturalenemies is often a long process that includes training in parasitoid rearing, establishing an efficientrearing facility, setting up (field) experiments and farmer training (Ooi, Dalat report, 1999).Success with such releases requires appropriate timing (the host must be present or the natural enemywill die or leave the area) and release of the correct number of natural enemies per unit area (releaserate). In many cases, release rates vary depending on crop type and target host density.This guide does not make specific recommendations about the purchase or release of the (commercially)available natural enemies, but it does provide information about the biology and behavior of somecommercially reared species that are important for cabbage pest insect control. This information couldbe helpful in making decisions regarding their use. See chapter 6. In addition, addresses of institutionsproviding or marketing natural enemies in Asia can be found in manuals such as “The BiopesticideManual” (BCPC, 1998) and on several sites on the Internet, for example that of the US department ofAgriculture, at www25 and www29 (see reference list).Cabbage Ecological Guide - 200060

Ecology of Insect Pests and Natural Enemies4.11 Management and control activities for pest insectsNext to biological control by natural enemies, pest populations may be managed by other methods. Theuse of insecticides is often used alternative but there are other options that may be valuable. Some ofthese options are listed in this section.Specific management and control practices, like many cultural methods, that are important for managingpest insect populations in the field are mentioned in the next chapter, for each pest insect individually.4.11.1 Use of insect nettingCultivation under “net houses” is increasingly receiving interest. A net house, or insect cage, is a frame ofwood a little higher than the cabbage plants, covered with fine mesh netting. The netting prevents insectsentering the crop from outside, particularly lepidopterous pests like moths and butterflies but also aphidsmay be prevented from entering the plants when the netting is fine enough. Net houses do not preventinsects coming from the soil like flea beetles. Often, the net houses are placed over nurseries, to preventdamage from caterpillars to the young plants. Also, in crops like tomato or hot pepper, net houses onnurseries can provide good initial control against aphids or whiteflies, which may carry virus diseases.Net houses may also be higher: about 2 - 3 meter. These can be used for both nurseries and productionfields. For good insect prevention, they need to be closed properly!Net house: plants in, pests out!Good experience with the use of a net house in eggplant was obtained from a field study in Bangladesh.A net house was made out of bamboo poles and nylon nets. Plant left-overs and pupae foundin the top layer of the soil were removed before placing the net house over the eggplants. Less insectinfestation of shoots and fruits was found on the net house plants as compared to the uncoveredplants.Unfortunately, some of the studies were not successful because the nets were stolen from thefield…! (pers. comm. Prabhat Kumar, 1999, Bangladesh).Although initial investment for preparing the net houses is high, savings from reduced sprayings canmake it interesting. When properly prepared and maintained, net houses can be used more than once.Inside a net house, the temperature may be a bit lower due to shading effect of the net and the humiditymay be a bit higher than outside. This may result in a quicker growth of the crop but it may also result insome more disease problems.Related exercises from CABI Bioscience/FAO manual:2-B.9. Roofing and screening of seed beds4.11.2 Use of trapsThere are several types of traps to catch insects. Most traps will catch adult insects. These traps areoften used for monitoring the populations rather than actual control. However, since some traps catchlarge quantities of insects they are often considered as control measures in addition to monitoring.61 Cabbage Ecological Guide - 2000

Ecology of Insect Pests and Natural EnemiesIf traps are used in isolation, information from them can be misleading. A low number catch will notindicate the timing of a pest attack, let alone its severity. Similarly, the number of insects caught in onecrop cannot be used to predict the number that will occur in other crops, not even when the crop are inadjacent fields.The most common types of traps used in the field are shortly described below.Pheromone traps: these are traps that contain a sticky plateand a small tube with a chemical solution called a pheromone.Pheromones are chemicals produced by insects that causestrong behavioral reactions in the same species at very smallamounts. They are usually produced by females to attract malesof the same species for mating. Such chemical is called ‘sexpheromone’.The males will fly to the pheromone trap and are trapped onthe sticky plate. Pheromones have been developed for severalvegetable pests including diamondback moth and armyworms(Spodoptera sp.). Pheromones are mainly used for detectingand monitoring pests, to a lesser extent for control of pestpopulations. One of the reasons is the high cost of pheromones.Light traps: Light traps are usually made of a light (can beelectronic, on a battery or on oil-products) switched on during thenight, and either a sticky plate or a jar filled with water or otherliquids. Insects (mainly night-active moths) are attracted to thelight, and are caught on the sticky plate or fall into the water anddie. Various types of traps are used, and they normally serve onlyas supplementary measures to other control methods. In China forexample, light traps are used for trapping and monitoring thepopulations of the cabbage moth, aphids and whitefly in bothgreenhouses and fields. When adult moths are found in the trap,look for egg masses and young larvae in the field. However, naturalenemies may also be attracted to light traps. When large numbersof natural enemies are caught it may be better to remove the traps.Pitfall traps: are plastic or glass jars,half-filled with water and a detergentlike soap, buried into the soil up tothe rim of the jar. These traps are goodfor catching ground-dwelling insectslike ground beetles. Purpose of thesetraps is purely for monitoring as manyground beetles are active during thenight and you may miss them whenmonitoring the field during the day.Pitfall traps may also be used withoutwater and detergent, to catch livinginsects for insect zoos. However, goodclimbers will escape.Cabbage Ecological Guide - 200062

Ecology of Insect Pests and Natural EnemiesYellow sticky traps: these are yellow colored plates, covered with glue or grease. They can also bemade from empty yellow engine oil jars and many lubricants are suitable as grease. The yellow colorattracts some insect species like moths, aphids, flea beetles and whitefly. The trap is especially suitableto monitor the adult population density. To a lesser degree, it can be used as a control measure, to catchadult pest insects. However, not only pest insects are attracted to the yellow sticky traps but alsonumbers of beneficial natural enemies. Thus, care should be taken when considering using sticky trapsand it would be advisable to place just one as a trial and monitor in detail which insects are caught. Iflarge numbers of natural enemies stick to the glue it might be better to remove the traps.Related exercises from CABI Bioscience/FAO manual:4.2. Sampling for arthropods with light trap4.3. Sampling for arthropods with sticky board4.4. Sampling for arthropods with water pan trap4.6. Soil-dwelling predators4.11.3 Use of threshold levelsThe decision to take control action against an insect population requires an understanding of the level ofdamage or insect infestation that a crop can tolerate without affecting the yield. Very often the termaction threshold level, economic threshold level (ETL), or tolerance level is mentioned. These terms areoften explained as “the level of infestation or damage at which some action must be taken to prevent aneconomic loss”. Traditionally, you had to look for the population of a certain insect in the field and whenthe population was higher than the value given for ETL, you were advised to spray.There are many formula to calculate economic thresholds. One of them is the following:cost of control (price/ha)ETL = ——————————————————————————————————-commodity value at harvest (price/kg) x damage coefficient (kg/ha/#pest/ha)The formula basically says that economic damage (=financial loss) begins at the point where costs ofdamage (yield loss due to insect/disease damage) are equal to the cost of control (costs of pesticides forexample).However, to actually calculate the threshold level for your own field situation is very difficult as most of thevalues that should be included in the equation are not known today, or can just be roughly estimated.That results in a very theoretical value! LThe thresholds vary with stage of crop growth, with costs of pesticides or labor, with environmental conditions,with market prices, etc., etc. and can therefore be very different for a region, for a season, for a field!However, in practice, most economic threshold levels are based on fixed infestation or damage levels.They do not consider the ability of the crop to compensate for (a large part of the) damage from neitherinsects nor the natural enemy population that may control the pest insect to an acceptable level. Manyother factors like weather conditions, personal health, etc. that are part of IPM agro-ecosystem analysis(AESA) are not considered in ETL values.63 Cabbage Ecological Guide - 2000

Ecology of Insect Pests and Natural EnemiesThe next table gives examples of a number of factors involved in decision making for ETL and for AESA.(picture from Fliert and Braun)ETLAESA● cost of control ● growth stage● harvest value of crop (estimation) ● weather conditions● loss of income due to pests (estimation) ● crop development factors (incl. compensation ability)● type and number of insect pests●●●●●●●●●type and amount of diseasestype and number of natural enemiestype and amount of natural disease control agentswater availability (irrigation, drainage)type and amount of weedssoil fertility statusfertilizer applicationsactivities in the field since last weekother observationsEconomic Threshold Levels may give a very general indication for the number of insects that canbe tolerated on a crop but they are seldom specific for the situation in your field today. Be verycritical to these threshold levels and monitor your field regularly to check for yourself in yourown field what decisions need to be taken4.11.4 Use of botanical pesticidesSome plants have components in the plant sap that are toxic to insects. When extractedfrom plants, these chemicals are called botanicals. Generally botanicals degrade morerapidly than most conventional pesticides, and they are therefore considered relativelyenvironmentally safe and less likely to kill beneficials than insecticides with longer residualactivity. Because they generally degrade within a few days, and sometimes within a fewhours, botanicals must be applied more often. More frequent application, plus highercosts of production usually makes botanicals more expensive to usethan synthetic insecticides. When they can be produced locally theymay be cheaper to use than synthetic insecticides. Toxicity to otherorganisms is variable, although as a group, they tend to be less toxic tomammals (with the exception of nicotine) than non-botanicals.Cabbage Ecological Guide - 200064

Ecology of Insect Pests and Natural EnemiesUsing botanicals is a normal practice under many traditional agricultural systems. A well-known andwidely used botanical is neem, which can control some insects in vegetables. In Vietnam, vegetablefarmers have utilized several botanical pesticides, including extracts from Derris roots, tobacco leavesand seeds of Milletia, which they claim to be effective.However, in addition to pest insects, some natural enemies may be killed by botanicals!A few commonly used botanicals will be briefly described below.Neem, derived from the neem tree (Azadiracta indica) of arid tropical regions,contains many active compounds that act as feeding deterrents and as growthregulators. The main active ingredient is azadiractin, which is said to be effectiveon 200 types of insects, mites and nematodes. These include caterpillars,thrips and whiteflies. It has low toxicity to mammals.Both seeds and leaves are used to extract the oil or juices. A neemsolution looses its effectiveness when exposed to direct sunlight and iseffective for only eight hours after preparation. It is most effective underhumid conditions or when the plants and insects are damp.High concentrations can cause burning of plant leaves! Also, naturalenemies such as Cotesia sp. can be negatively affected by neemapplications (Loke et al, 1992).Neem seed kernel extract: the recipeIn Ghana, Africa, neem seed kernel extract is used against insect pests on various vegetable crops.It has been tried on cabbage in a TOTs and FFSs and had a very good effect on diamondback moth(Plutella xylostella), probably due to the repelling action of neem.Here is their recipe:Pound or grind 30 g neem kernels (that is the seed of which the seed coat has been removed) andmix it in one liter of water. Leave that overnight. Next morning, strain or sieve it and use it immediatelyfor spraying. It should not be further diluted. Of course any neem preparation and spray applicationshould only be done after a previous AESA has shown the need for a neem application (pers. comm.Dr. J.Vos, 2000).Nicotine, derived from tobacco, is extremely toxic and fast acting on mostanimals, including livestock such as cows and chicken. It can kill people. Thenicotine of half a cigarette is enough to kill a full-grown man! In parts of WestAfrica, the tobacco plant is intercropped with maize because it is said to lowernumbers of borer insects on the maize. Nicotine kills insects by contact, and ifinhaled or eaten. The most common use is to control soft-bodied insects suchas aphids, mites and caterpillars.An additional danger of using tobacco leaf extract is that this extract may containa virus disease called Tobacco Mosaic Virus, or TMV. This virus disease affectsa wide range of plants, mainly solanaceous crops. When spraying tobaccoextract, chances are that you actually apply TMV!65 Cabbage Ecological Guide - 2000

NEcology of Insect Pests and Natural EnemiesRotenone is extracted from the roots of bean legumes, especially Derrissp. Rotenone is a contact and stomach poison. It is also toxic to fish,pigs and honey bees! It irritates the human skin and may causenumb feelings in mouth and throat if inhaled. Derris roots must bestored in cool, dry and dark places otherwise the rotenone breaksdown. Rotenone has very low persistence so once a spray isprepared it must be used at once.Pyrethrum is a daisy-like Chrysanthemum. In the tropics, pyrethrum isgrown in mountain areas because it needs cool temperatures to developits flowers. Pyrethrins are insecticidal chemicals extracted from thedried pyrethrum flower. Pyrethrins are nerve poisons that cause immediateparalysis to most insects. Low doses do not kill but have a “knockdown” effect. Stronger doses kill. Human allergic reactions are common.It can cause rash and breathing the dust can cause headaches andsickness.Both highly alkaline and highly acid conditions speed up degradation sopyrethrins should not be mixed with lime or soap solutions. Liquidformulations are stable in storage but powders may lose up to 20 percentof their effectiveness in one year. Pyrethrins break down very quicklyin sunlight so they should be stored in darkness.Pyrethroids are synthetic insecticides based on pyrethrins, but more toxic andlonger lasting. They are marketed under various trade names, for example Ambushor Decis. Some pyrethroids are extremely toxic to natural enemies! Pyrethroids aretoxic to honey bees and fish. Sunlight does not break them down and they stick toleaf surfaces for weeks killing any insect that touches the leaves. This makes themless specific in action and more harmful to the environment than pyrethrin. In additionthey irritate the human skin.Marigold is often grown in gardens for its attractive flowers. They arecultivated commercially for use as cut flowers. In addition, marigoldcan have a repellant effect on insects and nematodes.In Kenya for example, dried marigold when incorporated into the nurserysoil was found an effective treatment in terms of overall seedling health.Other experiments showed that fresh marigold tea repels DBM larvae,but for a few hours only (Loevinsohn et al, 1998).Chili, or chillipepper: the ripe fruits and seed contain insecticidalcompounds. Dried chili powder is highly irritant and difficult to workwith, but good results can be obtained on control of aphids invegetable gardens.In experiments in Kenya on botanical concoctions for aphid anddiamondback moth (DBM) control in kale, highly concentrated chiliCabbage Ecological Guide - 200066

Ecology of Insect Pests and Natural Enemiessolution treatments produced the same number of marketable leaves as the pesticide Karate (lambdacyhalothrin).Other studies from Kenya showed that chili sprays reduced pest numbers by 50% in the first week afterapplication but these built up again so farmers concluded from this experiment that chili needs to besprayed every 14 days for effective control (Loevinsohn et al, 1998). This probably applies for a periodwith low rainfall, as the solution will be easily washed off with rain.Garlic has been long known for its insecticidal activity. Garlic contains garlic oiland allicine, which have insecticidal and bacterial effect. It can be used as awater extract, for example in a solution of 0,5 l water with 100 garlic cloves, anda little soap. The price of garlic may make this recipe expensive. Garlic solutionsshould be tested on small plots first! Garlic can also be used as a seed coating,to prevent infection by soil-borne diseases or damage by soil insects. See section3.3.3. In some cultivation practices such as biological production, garlic issometimes used as an intercrop for other crops. Its strong odor may repel insects.See section 3.10.Despite being “natural” and commonly used in some regions, from thecharacteristicsNlisted above it is clear that botanicals can be very dangerous to use. Somebotanicals may be more dangerous to the user than chemical pesticides! Andin addition they may be very toxic for natural enemies.Always set up a study first on the effects of botanical pesticides on the ecosystemand on the economics. Do not just replace chemical insecticides with botanicals. Firstunderstand the ecosystem and how botanicals influence it!4.11.5 Use of mineral based pesticidesAsh from the remains of cooking fires is often used for general insect control. It seems that ashes canprotect leaves from chewing insects. The ashes must be crushed, then thinly and evenly spread. Thiscan be done by putting them into a coarse textured bag, which is shaken over the crop. Ashes providemore protection in the dry than in the rainy season. Another practice is to spread ash on nursery beds torepel ants, commonly done in Bangladesh. In Nepal, a mixture of mustard seed kernels (1 part) andashes (3 parts) is used against red ants. No research data are available to confirm this practice.When washed off the leaves ashes fertilize the soil very effectively. Wood ash is aknown source of potash and commonly used for fertilization of soils. Unleachedwood ash can contain around 5% potash in the form of potassium carbonate,which is alkaline and helps increase soil pH. Ashes contain small quantitiesof nitrogen and phosphorus in addition.Kerosene and fuel oil kill plants as well as insects. They can be usefulagainst insects that congregate. Nests of ants can be dipped. Spent motoroil can be used for this operation; the oil kills ants in seconds. The oil is veryflammable. Kerosene and fuel oil should not be used frequently and on largescale as it is detrimental to the environment.67 Cabbage Ecological Guide - 2000

Ecology of Insect Pests and Natural EnemiesThe Rationale of Biorationals….Insecticides may be divided into two broad categories: (a) conventional or chemical and (b) biorational.Conventional or chemical insecticides are those having a broad spectrum of activity and being moredetrimental to natural enemies. In contrast, insecticides that are more selective because they aremost effective against insects with certain feeding habits, at certain life stages, or within certaintaxonomic groups, are referred to as “biorational” pesticides. These are also known as “least toxic”pesticides.Because the biorationals are generally less toxic and more selective, they are generally less harmfulto natural enemies and the environment. Biorational insecticides include the microbial-basedinsecticides such as the Bacillus thuringiensis products, chemicals such as pheromones that modifyinsect behavior, insect growth regulators, and insecticidal soaps.4.11.8 Use of chemical pesticidesIf all other integrated pest management tactics are unable to keep an insectpest population low, then use of an insecticide to control the pest and preventeconomic loss may be justified. They can be relatively cheap, widely available,and are easy to apply, fast-acting, and in most instances can be relied on tocontrol the pest(s). Because insecticides can be formulated as liquids, powders,aerosols, dusts, granules, baits, and slow-release forms, they are very versatile.Types of pesticidesInsecticides are classified in several ways, and it is important to be familiar with these classifications sothat the choice of an insecticide is based on more than simply how well it controls the pest.When classified by mode of action, insecticides are referred to as stomach poisons (those that must beingested), contact poisons, or fumigants.The most precise method of classifying insecticides is by their active ingredient (toxic component).According to this method the major classes of insecticides are the organophosphates, chlorinatedhydrocarbons, carbamates, and pyrethroids. Others in this classification system include the biologicals(or microbials), botanicals, oils, and fumigants.Non-systemicsystemicVery often, pesticides are grouped into systemic or non-systemic products. Systemic pesticides aretaken up by plants through the roots, stems or leaves. Once inside the plant, systemic pesticides movethrough the plant’s vascular system to other untreated parts of the plant. Systemic pesticides can beeffective against sucking, boring and mining insects and nematodes.69 Cabbage Ecological Guide - 2000

Ecology of Insect Pests and Natural EnemiesNon-systemic pesticides are not taken up by the plant but form a layer on the sprayed insects or on plantparts.The advantage of systemic pesticides is that they can control pest insects that are difficult to reachbecause they are protected inside a plant, such as thrips. It is important to check the persistence (howlong it stays “active”) of such a pesticide. Most systemic pesticides should not be applied shortly beforeharvest because the pesticide may still be inside the plant or the fruit when it is harvested and eaten.4.11.9 WHO classification of pesticidesThe World Health Organization (WHO) has designed a classification table in which 4 toxicity categoriesfor pesticides are described. Most pesticides are classified by their potential risk to human health,usually based on acute oral LD 50levels. LD 50is based on experiments with animals and is the number ofmg of pesticide per kg of body weight required to kill 50% of a large population of test animals. Based onchemical data and tests, a chemical pesticide is classified in one of the four categories.Biological pesticides (biocontrol agents) such as Bt , NPV or Trichoderma are not included in the WHOclassification because the methods of testing the safety of these products are different from testingchemical pesticides.Table 4.11.9 : Examples of classification of some common pesticides available in Vietnam,Cambodia and Indonesia. Note that some pesticides are banned.Class IaExtremelyhazardousMethylparathion(Folidol)Mevinphos(Mevinphose)Alachlor(Lasso)Class IbHighlyhazardousMethamidophos(Monitor,Tamaron)Edifenphos(Hinosan)Dichlorvos(DDVP)Monocrotophos(Azodrim)Metomil(Lannate)(Murphy H., 1998, 1999 - unpublished)Class IIModeratelyhazardousFenitrothion(Ofatox)Dimethoate(Bi58)Cypermethrin(Sherpa, Vifenva,Cyrin)Fenvalerate(Sumicidin)Deltamethrin(558)Fenobucarb(Bassa)Cartap(Padan)Fipronil(Regent)2,4-DEndosulfan(Thiodan, a.o.)Fluvalinate(Maverik)Paraquat(Gramoxone)Class IIISlightlyhazardousTrichlorfon(Dipterex)Dicofol(Kelthane)Class IV*unlikely topresent acutehazard in normaluseKasugamycin(Kasai)ZinebValidamycin A(Validacin)Diafenthiuron(Pegasus)Atrazin(Gesaprim,others)Benomyl(Benlate)ManebCabbage Ecological Guide - 200070

Ecology of Insect Pests and Natural Enemies4.11.10 Pesticides and health in IPM trainingIn a few countries in Asia, a health component has been added to IPM training programme. Previously,health studies were aimed to change national pesticide policies. While some of the more hazardouspesticides were banned or restricted, frequently these were not enforced. Therefore in the IPM tradition,health studies were redesigned to allow farmers to conduct their own studies to change farmer’s ‘personalpesticide policy’.Farmer groups in Cambodia, Vietnam and Indonesia are conducting health studies within their owncommunities among their fellow farmers that include:* Analysis of the chemical families and WHO health hazard categories of the pesticides in use (andor available in local pesticide shops).* Analysis of the numbers of pesticides (and types) mixed together in one tank for spray operations.* Analysis of liters (or approximate grams) of pesticide exposure per season or year.* Field observations of hazardous pesticide handling.* Interviews and simple examinations for any signs and symptoms of pesticide poisoning: before,after and 24 hours after spraying.* Household surveys to determine hazardous pesticide storage and disposal practices andoccurrences of pesticide container recycling or repackaging.Children who are participating in IPM schools are also conducting similar studies with their parents andneighbors through the Thai and Cambodian government educational programs.Through the experience of gathering, analyzing and presenting this data back to fellow farmers, a morefundamental understanding of the health as well as the ecological hazards of inappropriate pesticide useis gained. These studies motivate farmers to join IPM, sustain IPM principles on better field observationbased decision making on pest control, and also can be used to measure the impact of IPM. Forexample, the Vietnam IPM program is measuring the impact of community IPM by conducting healthstudies before and after initiating community IPM in 4 areas.This is especially critical to vegetable IPM where the most indiscriminant use of pesticides is occurring.Too many chemical products are mixed and applied together too often during a single growing season.This results in numerous cases of mild to moderate pesticide poisoning among the farmers, increasedpest or disease resistance, and significant disruptions to the local ecology.Pesticides and health: some unhealthy figures…..Indonesian shallot farmers were mixing up to 9 different products in one tank (average 4) and spraying2-3 times per week (Murphy, 2000). The Cambodian farmer is mixing on average 5 pesticides pertank that is applied up to 20 times per season (Sodavy et al, 2000). Up to 20% of all spray operationswere associated to witnessed pesticide poisoning among wet shallot farming in Java (Kishi et al, 1995).During a single spray session among Sumatran women (of whom 75% were using a extreme, high ormoderately hazardous to human health pesticide), 60% had an observable neurotoxic sign of pesticidepoisoning (Murphy, in press). In an IPM farmer conducted survey in Cambodia among 210 vegetablegrowers, 5% had a history of a serious poisoning event while spraying (loss of consciousness) andanother 35% had a moderate episode.71 Cabbage Ecological Guide - 2000

Ecology of Insect Pests and Natural Enemies4.11.11 Pesticide associated problems on insects and natural enemiesDespite the advantages of conventional insecticides, there are numerous problems associated with theiruse. These include:1. The resurgence of pest populations after elimination of the natural enemiesA well-known phenomenon is that when natural enemies are killed by pesticide applications, pestinsects (which often have a high reproduction rate) can increase their numbers very quick. Thiseventually results in yield and quality loss of the crop. Even pest insects that, under no or lowpesticide applications cause no problem (populations are kept low by natural enemies) can causeoutbreaks and yield loss when natural enemies are eliminated, especially insects or mites thathave developed resistance against pesticides. An example is red spider mite, which has manynatural enemies but can cause severe problems in heavily sprayed fields.2. Development of insecticide-resistant populationsThe development of resistance is one of the moreserious problems in pest management.Resistance means an insect can tolerate apesticide without being killed. Many insect pestspecies now have resistance to some or severaltypes of insecticides, and few chemical controloptions exist for these pests.The number one resistant insect is the aphid,Myzus persicae (Homoptera: Aphidae). Thisaphid is resistant to more insecticides than anyother insect. The numbers two and three notoriously resistant are the Colorado potato beetle,Leptinotarsa decemlineata and the diamondback moth, Plutella xylostella. One case ofdiamondback moth resistance against pesticides is described in the box below. In some areas,the diamondback moth has even become resistant to biological control agents like Bt (Bacillusthuringiensis).3. Negative impacts on non-target organisms within and outside the crop systemNumerous cases exist of negative impact of pesticides on humans and livestock. Many farmersparticipating in FFSs have experience with pesticide poisoning, or side-effects on health frompesticides.LNatural enemies are generally more adversely affected by chemical insecticides than the targetpest. Because predators and parasitoids must search for their prey, they generally are very mobileand spend a considerable amount of time moving across plant tissue. This increases the likelihoodthat they will get in contact with the pesticide. They also feed on or live inside poisoned prey. Inaddition to killing natural enemies directly, pesticides may also have sublethal effects on insectbehavior, reproductive capabilities, egg hatch, rate of development, feeding rate, and life span.Cabbage Ecological Guide - 200072

Ecology of Insect Pests and Natural EnemiesThe case of DBM resistance in Cordillera Region, Philippines.Over the years, diamondback moth (DBM) had become resistant to most availablepesticides in the Cordillera region in the Philippines. Human poisoning incidents dueto spraying of cyanide on cabbage in farmers’ desperate attempt to control DBM, were amajor reason to start a project. Collaborators of this project were ADB (donor), the InternationalInstitute of Biological Control (now integrated in CABI Bioscience), Philippines Dept. of Agriculture(Cordillera Region), Benguet State University, and Local Government Units in Benguet and MountainProvinces. The project aimed to transfer proven IPM practices to vegetable farmers in the Cordilleraregion, to reduce agrochemical input use, particularly of toxic insecticides, and to promote IPM asthe standard approach to pest and crop management in cabbage and potato.The project reached 1719 farmers in 65 FFS groups (average farm size 1ha).Impacts of the project (1994 – 1996) included:· Cabbage yield increased by 4.8t/ha (21% increase) in dry season cabbage· Potato yield increased by 3t/ha.· Decreased production costs/ha of cabbage (11%) and potato (2%)· Before training, 100% farmers used insecticides, after FFS only 25% using insecticides and notfor DBM.· Before FFS , 80% farmers preferred Category I and II highly toxic products. After FFS, 90%farmer shifted to Category IV products with lower mammalian toxicity and biopesticides· Due to successful biological control of key pest DBM (through parasitoid Diadegma sp.), manyfarmers now produce insecticide-free cabbage and consumers no longer worry about residues.· Conservation of native natural enemies encouraged. More species diversity in IPM fields thanregularly sprayed fields (159 vs.125) and lower proportion of pests· Net income of FFS farmers increased by 17 %· 80% average decrease in insecticide use (13.8 to 2.9l cabbage crop) in dry season and 55% inwet season.· Farmers rely less on agrochemical salesmen and more on own knowledge and other farmers forpest management information.· Synthetic fertilizer rate halved without negative effect on yield while organic fertilizer rate maintained.(CABI Bioscience. TSG IPM Analyses No. 6: Impact of Farmer Field School training on natural,human and social capital: case studies from the Philippines and Kenya)Related exercises from CABI Bioscience/FAO manual:1.3 Spray dye exercise1.4 Effect of pesticides on spiders and other natural enemies1.5 Role play on insecticide resistance4-A.13 Comparison of biological and chemical pesticides used in caterpillar control4-D.8. Spot application of acaricides to manage mites73 Cabbage Ecological Guide - 2000

Major Cabbage Insect Pests5MAJOR CABBAGE INSECT PESTSSUMMARYThe diamondback moth (Plutella xylostella) is the major pest insect of cabbage, inboth temperate and tropical areas in Asia. Other pests such as webworm (Hellulaundalis), heart caterpillar (Crocidolomia binotalis), and white butterflies (Pierissp.) can locally be severe. Flea beetles (Phyllotreta sp.), aphids (Brevicorynebrassicae), and cutworms (Agrotis sp.) can be a problem in nurseries. Stemborer(Melanagromyza cleomae) is a relatively “new” pest but appears to occur on awider scale in Asia than so far reported in literature.Biocontrol options exist for many insect pests of cabbage, such as Diadegmaparasitoids for diamondback moth control, NPV virus for armyworm (Spodopterasp.) control, and Bt (Bacillus thuringiensis) applications against various caterpillars.Other naturally occurring biocontrol agents, such as predators (ladybeetles, spiders),parasitoids and pathogens (e.g. fungi killing aphids or webworm) can locally,and in some seasons, give additional control.Most biocontrol options should be part of an IPM programme that includes farmertraining.Several cultural practices such as weed removal, removing infested plant material,use of trap crops, and hand-removal of egg-masses and larvae can provide additionalinsect control. For several cabbage insect pests, insecticide use is not effectivenor economical and may in some cases (e.g. whitefly) even aggravate pest problems.Most insect management options focus on prevention of high populations, andbiocontrol, either by conserving and augmenting naturally occurring natural enemies,or by releasing/applying biocontrol agents.Cabbage Ecological Guide - 200074

Major Cabbage Insect PestsIn the following sections an indication of the duration of parts of the insect’s life cycle is given. It isemphasized that these figures are indications only as they depend on local climate and season. Ingeneral: the warmer, the quicker the insect’s life cycle. The actual duration of the life cycle of a specificinsect or natural enemy from your area can be checked by setting up an insect zoo experiment (seesection 4.3).5.1 Diamondback moth - Plutella xylostellaThe diamondback moth is a major pest of cruciferous vegetable crops in both temperate and tropicalareas. It attacks a wide range of wild and cultivated cruciferous crops.DescriptionAdult moths are about 6 –10 mm long. They are grayish-brown in color and havethree light brown to white, triangular marks on the edge of each forewing. Whenthe moth has settled at rest, marks join together to form three diamond shapesalong the middle of the back. This is why the moth is called diamondback moth.Usually, the females are lighter colored than the males. The moths are poor flyersbut they are often transported long distances on the wind. Moths are more activeand visible at dusk. They fly around plants searching for a mate or a place todeposit eggs.Eggs are very small, less than 1mm and yellow in color. They are laid eitherindividually or in small groups under the leaves near the center line of the leaf, orclose to the leaf veins.The caterpillars can be up to 13 mm long. DBM caterpillars varyin coloration from a light brown at hatching to dark green whenfully grown. The body can have white patches and black spots.Caterpillars usually feed on the underside of leaves.First instar caterpillars feed as leafminers inside the plant tissue.The three later instars feed on the underside of leaves. They donot eat the veins and often leave the upper skin of the leaf intact,which leaves a window-like appearance. If disturbed, they wriggleaway quickly and drop from the leaf on a silk thread. They climbback on the leaf on this thread once the danger has passed.Fully-grown caterpillars spin a greenish cottony cocoon of about10 mm long on the underside of the leaves or in litter under theplant. The silk mesh is added to the surface of the leaf making itsremoval difficult.Life cycleThe life cycle can be completed in one to two weeks, dependingon the temperature. Generally, the higher the temperature, thequicker the life cycle and the more generations of DBM are formed.In the tropics, the life cycle is shorter in the lowlands than in themountains.75 Cabbage Ecological Guide - 2000

Major Cabbage Insect PestsDiadegma semiclausum is mass-produced in rearing facilities in the highland areas of many countries inSoutheast Asia. See box below for an example.Diadegma semiclausum in the PhilippinesFarmers in the mountain province Cordilleras applied insecticides for DBM control 24 to 32 timesduring the dry season and 18 times during the wet season. DBM had become resistant to manypesticides and farmers were resorting to highly toxic compounds. When the National IPM Programwas implemented and the parasitoid Diadegma semiclausum was introduced, many of the farmersreduced their pesticide application to only 2 times, for control of other pests. Diadegma is beingreleased into cabbage fields at regular intervals. It can survive by transferring to neighboring fields aslong as farmers do not spray chemical insecticides.It should be noted that farmer training is an essential element in the success of Diadegma.(FAO-ICP Progress report ‘96 – ’99)· Diadegma insulareThe parasitoid Diadegma insulare is better adapted to warmer conditions andmay play a major role in controlling DBM in areas that are too warm for D.semiclausum. Diadegma insulare from Florida (USA) was recently introducedin the Philippines for DBM control under lowland conditions. Currently, parasitoidrearing methods are being studied and small scale experiments under nethouseconditions are being done.· Cotesia plutellaeThe parasitoid Cotesia plutellae is also better adapter to warmerclimates than Diadegma semiclausum. Cotesia plutellae is massproducedin countries like the Philippines for field releases anddemonstrations in farmers’ fields. Cocoons are used for field release(FAO-ICP Progress report ‘96 – ’99).However, Cotesia plutellae is found a less effective parasitoid thanDiadegma semiclausum because it performs well at high DBMdensities, but not so well when DBM populations are low. Therefore,introduction of Diadegma insulare for the lowlands is being considered by Vietnam and Philippines(pers.comm. Mr.J.W.Ketelaar, Vietnam, 2000).· Diadromus collarisA parasitoid that was introduced into Vietnam is Diadromus collaris. This little wasp parasitizes thepupae of DBM. Diadromus was released in cabbage fields in highland areas of Dalat, Vietnam in 1998.Monitoring and ecological studies were conducted by Farmer Field Schools and farmer study groups(FAO-ICP Progress report ‘96 – ’99). However, Diadromus collaris has not established yet (Ooi, 1999).Diadromus collaris is established in highland areas in Malaysia (Cameron Highlands).77 Cabbage Ecological Guide - 2000

Major Cabbage Insect Pests· Other parasitoidsSeveral other species of parasitoids have been recorded on DBM. These include the larval parasitoidMicroplites plutellae, which is common in North America, and Apanteles ippeus, which is widely distributedin eastern Australia (CABI Dossier Diadegma insulare).Other parasitoids can occur naturally in certain areas and may play a role in reducing damage from DBMinfestation when (broad-spectrum) insecticides are not intensively used. In general, their levels of parasitismare relatively low.· PathogensA number of pathogens are known to kill DBM. The most common ones are the fungi Entomophthorablunckii and Entomophthora radicans. Other DBM-pathogens are Paecilomyces fumosoroseus, andZoophthora radicans . DBM caterpillars can also be killed by a granulosis virus, and a nuclear polyhedrosisvirus (NPV). Except for Bt, there are restrictions on the effectiveness of these pathogens since they needspecific conditions (temperature, humidity) to be active (Ref. www12).Commercial preparations of Bacillus thuringiensis (Bt) can effectively control DBM caterpillars as well assome other caterpillars. It should be noted here that in some areas resistance to Bt has been found. UseBt only on the basis of careful field observations. Care should be taken that Bt is not used very frequently,and that different brands are rotated. Bt kills DBM larvae slow: only after about 3 days. However, affectedlarvae stop feeding on the crop after a while. Thus, although alive, they do not damage the crop anymore.See also section 6.3.1 on Bt.· PredatorsPredators may also play a role in the control of DBM. For example, spiders,lady beetles, lacewings (Chrysopa sp.) and some beetles are reported toattack DBM. These predators tend to build up only in the later part of thecropping season. Efficiency of predators varies greatly between sites.Management and control practicesPrevention activities:· Although there seem to be differences in susceptibility to DBM attacks in different varieties ofcabbage, no resistant variety is known to date. Due to the many generations that DBM canproduce in a season, resistance may be broken down very quickly.· The adults can be monitored with pheromone traps. Pheromone-impregnated strips are also beingtested that disrupt diamondback mating.· It is preferable to plant cabbage in the rainy season when the population of DBM is deterred by therain.· Intercropping with tomato (or other crops not susceptible to DBM) may help reducing populationsof DBM. The idea of intercropping is that DBM adults will have more difficulty in finding cabbageplants when these are camouflaged between other crops. See section 3.10.1.Cabbage Ecological Guide - 200078

Major Cabbage Insect PestsTrap cropping for DBM control in IndiaIn India trap crops are being used in IPMFarmer Field Schools. The trap crop used wasmustard. The recommendation of the IndianFFS is to sow two rows of mustard after every9 rows of cabbage. The first row of mustardshould be sown 15 days before the cabbageis transplanted and the second row of mustardabout 15-25 days after transplanting thecabbage. Diamondback moth prefers mustardto cabbage. The trap crop was also an effectivetrap for other caterpillars and aphids (Srinivasan, 1991). Whether or not the mustard needs to sprayedor destroyed to remove the pest insects, is disputable. This can be tested in a study.· Sometimes, planting a trap crop around the field helps to control DBM. The trap crop, whichshould be established before the cabbages are transplanted, will attract pest insects. These pestinsects in addition, will attract natural enemies. The trap crop is either destroyed together with theDBM larvae or left in the field as a “natural enemy reservoir”. See box above and section 3.10.2.These trap crop plants should be monitored with more frequency than the main crop and requirecontrol of the DBM before it can be passed to the main crop. Unattended trap crops can generatelarge populations of DBM! Special care is needed to manage these crops to use them as part ofa control practice.In fact, several researchers report that combining trap crops with release of parasitoids is a verygood DBM management practice. See example in box below.Combining trap crops with release of parasitoidsFor highland areas the Indian Institute of Horticultural Research (IIHR) advises to grow the boldseededIndian mustard as a trap crop. This attracts up to 80% of DBM, and should be sown thicklyall around the area where crucifers are to be grown, at least 10 days before the cruciferous cropsthemselves. Releasing the parasitoid Diadegma semiclausum on the 16th and 21st days after planting.The recommended number of parasitoids to release is 3,000 pupae per hectare per release date in acrop cycle of 70 - 80 days. Spraying with 4% neem seed kernel extract (NSKE) once every threeweeks, if necessary, to help control aphids. NSKE can be sprayed onto the mustard to control DBMand aphids. Not more than 3 NSKE sprays are required (ref. www22).For lowland areas, the following research results were good:Planting collards as a trap crop in and around cabbage fields lured a significant number of DBMadults away from the cabbage. Supplemental releases of Cotesia plutellae in the collard plantingswould allow this parasite to build its numbers along with Diadegma insulare, and both species couldspread into the cabbage to attack DBM larvae. This approach could greatly reduce grower costs asfewer C. plutellae parasites would need to be released, and the number and frequency of pesticideapplications also would be reduced. This strategy also would provide less opportunity for DBM todevelop resistance to pesticides (ref. www23).79 Cabbage Ecological Guide - 2000

Major Cabbage Insect PestsOnce DBM is present in the field:· Where effective natural enemies are present, a few DBM larvae are necessary to maintain thepopulation of natural enemies. Trying to eradicate all DBM larvae may actually reduce the naturalenemy population.· Parasitoids released in cabbage fields have proven to be able to effectively control DBM as longas no pesticides are used. Release should be part of a larger DBM management programmethat includes farmer training.· Where irrigation facilities exist, water sprays may be used to control DBM. Overhead irrigation,especially when applied during dusk, interferes with mating and oviposition of DBM. In addition,young larvae may be washed off the leaves and drown. Overhead irrigation may have a negativeimpact on disease that can generally spread more easily with splashing water from irrigation.· When after careful monitoring the field, and comparing numbers of natural enemies and pestinsects, it is found that natural enemies in the field are not controlling DBM sufficiently, applyingBacillus thuringiensis (Bt) may be considered. Bt is safe for most natural enemies and, if appliedcorrectly, will provide effective control of DBM (Note: in some areas DBM has developed resistanceagainst Bt!). It should be noted that DBM larvae that are parasitized by parasitoids like Diadegma,will also be killed by Bt sprays! In addition, Bt should be rotated to decrease the chance that DBMdevelops resistance to Bt.· In some countries, certain botanical insecticides like the extracts of the neem tree, have beenfound effective against DBM on cabbage. It is recommended to test these botanicals in small trialareas first before applying them full scale. There may be negative side-effects on natural enemypopulations. See section 4.11.4. and box in section 4.9.· Removing all crop debris after harvest helps to reduce populations. The cabbage leaves can beused to feed farm animals, or put on a compost pile. DBM can survive in plant residues andmigrate to the next plot.· Pesticide use for DBM control is not recommended. See box below.· A new method of insect control now in the experimental stage is to attract adults to a trap wherethey are infected with a pathogen before exiting. Researchers in England have developed specialtraps that allow diamondback moths to enter the trap, pick up the fungal pathogen Zoophthoraradicans and then exit the trap. The moth then carries the pathogen to the crop where it can infectboth moth larvae and other adults (Peet, www10).Cabbage Ecological Guide - 200080

Major Cabbage Insect PestsThe sad story of chemical control of DBMChemical control has been the major control tactic used in the past. Due to the many generationsthat DBM can produce in a season, it can also develop resistance to insecticides very quickly. Moreand more, insecticides became ineffective in controlling DBM. Some insecticides to which DBM hasdeveloped resistance include cypermethrin, deltamethrin, fenvalerate, diazinon, permethrin andphenthoate. For example, in Taiwan,DBM has developed resistance against33 out of the 34 available insecticides!It seems like the insect could developpesticide resistance more quickly thanthe chemical industry could developnew pesticides!Due to the ineffectiveness ofinsecticides, farmers began to spraymore often, at higher doses, with differentchemicals and with mixtures andcocktails of pesticides. The result?Higher costs for farmers to buy thepesticides, more health risks from applying sometimes very dangerous chemicals, more environmentalpollution and eventually more resistance of DBM against these pesticides. The big winner of thegame? DBM! Still a major pest in many regions. The other winners of the game? Other insects suchas armyworms and the cabbage webworm, once minor pests of cabbage, could become majorproblems because all natural enemies were destroyed.¤Points to remember about diamondback moth:1. Diamondback moth (DBM) is the most serious pest of tropical cabbage areas.2. Very effective biological control of DBM is possible through parasitoids.3. Parasitoid release should be part of a larger IPM programme, that includes farmer training.4. Pesticides are not effective for DBM control.5. Natural enemies are killed by pesticides.6. Bt is usually very effective for DBM control, but brands should be rotated (resistance!).Related exercises from CABI Bioscience/FAO manual:4-A.14-A.2.4-A.3.4-A.4.4-A.5.4-A.6.4-A.7.4-A.8.4-A.124-A.13Life cycle of caterpillar pestsDiamondback moth injury symptoms on cabbagePlant compensation studyAssessment of impact of ground-dwelling predatorsMeasuring the parasitism level of caterpillarsParasitisation on diamondback moth of cabbageEffect of parasitisation on feeding behavior of diamondback mothRainfall as mortality factorMixed cropping examples: tomato/beans and cabbage/mustardComparison of biological and chemical pesticides used in caterpillar control.81 Cabbage Ecological Guide - 2000

Major Cabbage Insect Pests5.2 Aphids - Brevicoryne brassicaeDescriptionCabbage aphids are a serious pest on most cruciferous crops including a wide range of cruciferousweeds.(from Stoll, 1987)The wingless aphids are up to about 2.5 mm long, grayish-green in color, with a dark head and blackstripes on the body. The aphid is covered with a grayish-white colored waxy powder, which is alsosecreted onto the surface of host plants.The winged aphids are slightly longer than the wingless ones and have a dark-colored head and body.The veins on the wings appear brown in color. The aphids have small syphons (looking like small antennae)at the back of their body. Syphons are a good way to recognize aphids.Colonies of these aphids are usually found on the undersides of cabbage leaves.Unlike other aphid pests of vegetables, the cabbage aphid is a one-host aphid : it remains on cruciferouscrops throughout its life.The aphids can reproduce asexually: that means that males and females do not have to mate in order toproduce young. One female gives birth directly to small nymphs. That means large numbers of aphidscan be produced in a very short time! Only in cool areas, eggs are produced after mating. The eggsoverwinter and young nymphs emerge when the temperature rises. All winged aphids are females. In thetropics, most unwinged aphids are probably also females. Most reproduction in the tropics will be asexualso males are not needed.Life cycleIn the cooler areas of its distribution, the cabbage aphid overwinters as small, shiny black-colored eggslaid particularly around leaf scars of stems of plants that remain in the field throughout the winter. Whenthe temperature rises, the aphids hatch and colonize the new emerging flowering stems or harvestedvegetable crops that have not been ploughed in. Then, winged aphids fly away to colonize new hostplants. They produce wingless aphids. These aphids produce more young aphids that form new colonies.They feed on the tender, actively growing shoots and leaves, often on the underside of leaves where theyare protected from the sun and rain. When aphid numbers outrun food supply, winged forms reappear andmigrate to nearby plants to renew the growth cycle. This happens regularly during the growing season.Warm, dry weather favors a rapid build-up of aphid colonies.Cabbage Ecological Guide - 200082

Major Cabbage Insect PestsPlant damage and plant compensationThe first signs of attack are small bleached areas on the leaves of infested plants. The leaves then turnyellow and become crumpled. The aphid colonies are protected inside the crumpled leaves. The effectsof infestation are worst on seedlings and young plants. They can be stunted and may die in unfavorableweather. Early damage to the growing point of a cabbage plant distorts the head. Even when youngplants are infested only lightly, the leaves of the plants when they are mature continue to show signs ofthe original attack. Infestations on larger plants may reduce yield and also spoil the plants by contaminatingthem with wax, cast skins and honeydew. Honeydew is the excretion of aphids. It is slightly sweet andis excreted from the syphons. Honeydew can make the leaves sticky and several fungi species grow onthe honeydew producing black marks on the surface of the cabbage. This lowers the quality. Wheninfestation is large, the aphids sometimes penetrate the heart of the cabbage.Aphids tend to be very localized: they usually colonize just a few plants but can be very abundant oneach plant.In addition to the direct crop damage, cabbage aphids also transmit the cauliflower mosaic virus and theturnip mosaic virus to cruciferous crops. Good crop hygiene (uprooting and destroying the virus infectedplants), rather than trying to kill the aphids, is the only way of reducing the impact of these viruses as thetime taken by virus-carrying aphids to infect new crops is often less than one minute. This is too short tokill the aphids by any control practices.Aphids as milk cows for ants...?!Ants are attracted to aphid colonies because the aphids produce honeydew whenthey are disturbed. Ants like to eat the sweet honeydew. The ants keep and sometimeseven protect the aphid colonies. They “milk” the aphids to get the honeydew.Although ants can be natural enemies of some pest insects, in this case, ants cannot beconsidered as natural enemies of aphids because they do not kill aphids but may in fact protectthem.Natural enemiesThe weather is a major natural agent restricting the build-up of cabbage aphid infestation in cold, temperateregions and mountainous areas. In dry, warm seasons the aphids can often produce extremely largeinfestations whereas in wet, cool seasons the aphid population remains small. In a period of frequentrain, aphid populations will be very low if not absent.Predators such as lady beetles and hover flies (Syrphids) and parasitoids like the wasp Diaeretiella rapaeare important natural enemies of the cabbage aphid.In wet seasons, outbreaks of fungi that killaphids may occur. This often coincides withperiod of high humidity and rain. Dead aphidsmay be seen covered with white coloredfungus growth on the body. These fungi canspread quickly to reduce aphid populations.See chapter 6 for details on these naturalenemies.LarvaeLady beetle : an important predator of aphidsAdult83 Cabbage Ecological Guide - 2000

Major Cabbage Insect PestsManagement and control practicesPrevention activities:· Healthy, quickly growing plants are the best way of preventing many pests and diseases. Aphidinfestation often occurs when plant condition is slightly poor, for example just after transplanting,or when too much or too little fertilization is added or when the soil structure is poor.· Host plant resistance: There is little chance of producing a cabbage variety with a durable resistanceto cabbage aphids. This is because there are many biotypes (individuals with slightly differentcharacteristics) of aphids present in the field and new biotypes can form regularly. It is very difficultto produce a variety that has a resistance against all these biotypes.· Cultural control: Cruciferous plants that remain in the field after harvest are largely responsible forlarge numbers of eggs and/or adults staying over. Therefore, the most effective prevention andcontrol measure is to eliminate as many of these sources of infestation as possible to prevent theaphids from spreading to the new crop. The crop left-overs can be buried into the soil, fed to farmanimals, added to a compost pile or collected, slightly dried and burnt. Removing crop left-overs isalso very valuable for disease prevention.· Undersowing with clover may help to reduce aphid infestation. In a study where cabbage wasundersown with white clover, cabbage aphid population was reduced with 90%! (Finch, 1996). Seesection 3.5.3.4 on organic mulch.Once aphids are present in the field:· Monitor the field regularly to check population growth. Cabbage aphid population build up rapidlybut locally. It is important to examine plants regularly, both in seedbeds and in the field. Whenaphids are found but the number of infested plants is low and at the same time there are naturalenemies like lady beetles present, no additional control measures are necessary.· On a small scale, aphids can be washed off the plants with water or rubbed by hand.· Small populations can also be removed by removing the infested leaves by hand and destroyingthese.· When large populations of aphids are present in the field at an early stage (newly transplanted oryoung plants) and the weather is warm and dry, chances are that the aphid population will expandvery quickly and causes damage to the growing points of the plants. Monitor the field carefully forpresence of natural enemies (particularly note lady beetles and aphid “mummies” (see sections6.1.1 and 6.2.1)). When there are large numbers of natural enemies, do not apply insecticides butcontinue monitoring. When natural enemy populations are low compared to the aphid population,consider localized sprays. See next paragraph. Also see section 4.8 on natural enemy efficiency.· Soap solutions (concentration of 0.5 % (5 g per liter)) kills aphids instantly. See section 4.11.6.· Botanicals such as neem solutions may control aphids. Good results are obtained from variouslocations. See section 4.11.4.· Biopesticides: see box below for an example from Bangladesh.Cabbage Ecological Guide - 200084

Major Cabbage Insect PestsJ Free biopesticides for aphid controlDuring a TOT in Mymensingh, Bangladesh, the newly transplanted eggplant field suffered from aphidinfestation. Participants from the TOT discovered aphids covered with fungus on various locationsaround their eggplant field. They collected as much diseased aphids as they could get, mixed themin water, and stirred firmly. This will release spores from the fungus into the water and this waterbecomes infectious for aphids. Then the solution was slightly filtered through a cloth (to remove largeparts) and sprayed on the eggplants using normal backpack sprayers (pers. comm. Prabhat Kumar,1999).· Localized sprays. There are insecticides that control aphids. However, spray applications ofinsecticides can kill lady beetles and many other natural enemies of the cabbage aphid and otherpest insects! Balance the benefits of spraying against the harm done to the beneficials! Whenapplying insecticides is considered necessary, apply only on those plants that have aphid colonies,not on all plants. This reduces the amount of pesticides needed and, may save at least part of thebeneficials present in the field.¤Points to remember about aphids:1. Aphids have many natural enemies.2. On small scale, aphids can be removed by hand rubbing, washed off with water spray, or destroyedby removing and destroying infested leaves.3. Localized (infested plants only) spray with soap solution (0.5%) controls aphids.4. Biopesticides, where available, may offer good control.5. Insecticides are usually not necessary for aphid control.Related exercises from CABI Bioscience/FAO manual4-D.1 Predation on sucking insects in insect zoo4-D.2 Cage exclusion of natural enemies in the field5.3 Flea beetle - Phyllotreta sp.The main host plants for flea beetles are cruciferous crops but they can also live on cotton and cereals.DescriptionThere are many species of flea beetles that damage cruciferous crops, most of them belong to the genusPhyllotreta. The adult beetles can be separated by color into two major groups: one in which the back isblack with two longitudinal yellow bands (the striped flea beetle) and the other group in which the back isof one color, usually black. All adults have backs with ametallic appearance and are about 1.5 - 3.0 mm long.Flea beetles are characterized by their enlarged hindlegs with which they make long flea-like leaps. As theirname implies, flea beetles have the habit of jumpingwhen disturbed.P. cruciferae P. nemorumLife cycle85 Cabbage Ecological Guide - 2000

Major Cabbage Insect PestsThe adults can overwinter in sheltered sites where leaf litter and plant debris is present. They becomeactive with temperatures rising above 20 o C. When the temperature is always high, like in tropical lowlands,the flea beetles will not have a resting phase but just continue reproducing.Adults disperse, frequently in large numbers, on prevailing winds. They can travel long distances. Whenthey locate a suitable host crop, they settle and start to feed, often on seedling tissues below ground.After mating, the beetles lay their eggs in the soil near host plants. The eggs are pale-yellow in color,about 0.3 mm long and 0.15 mm wide. The larvae of all species are generally white or pale-yellow in colorand have very short legs. The larval head is dark in color. The larvae of most species feed on the plantroots. After living in the soil for about 4-5 weeks, the fully grown larvae are about 5-6 mm long. Theypupate in the soil. The pupa is about 2.5 mm long, white to yellow in color at first but later turns darker.The duration of the pupal stage depends on climatic factors like the temperature, it may take up to 4weeks.Plant damage and plant compensationDamage by flea beetles is most evident on seedlings. Severe damage can be caused by beetles feedingon the seedlings below soil surface, before the seedlings emerge above the soil. With emerging seedlings,the beetles chew holes, particularly in the cotyledons (seed leaves), giving them a characteristic shotholeappearance. Occasionally, seedlings may be completely destroyed. Loss can be greatest in a dryperiod when the seedlings grow very slowly after germination.Flea beetles are especially damaging to Chinese cabbage, which is sometimes used as a trap crop tokeep flea beetles off other crucifers.Apart from the direct damage they cause, flea beetles can also transmit turnip yellow and turnip mosaicvirus. Crops are at risk mainly when the new generations of flea beetle emerge. Although the plants areby then large, damage may be severe if large numbers of beetles enter the crop.Plant compensation study example for flea beetle damageHow much leaf damage can cabbage seedlings sustain? When does crop injury result in yield orquality loss? How much damage can be tolerated before something has to be done to control fleabeetles? Find out in a compensation study!Select a number of seedlings (e.g. 100) in a separate area of the nursery. Cut different percentages ofthe seedleaves (cotyledons) and different percentages of the first true leaves at different times. Forexample: cut 10, 25, 50 and 75% of the cotyledons one week after emerging, another 10, 25, 50 and75% of all leaves per plant at 2 weeks after emerging, etc. Cutting the leaves will simulate the damagedone by flea beetle (and some other leaf-eating insects). Label the different “treatments” carefully toavoid mixing up. Transplant the seedlings in a separate area of the field and include plants that havenot been cut as the control. Compare plant vigor, yield and quality during growing and at harvest time.Natural enemiesThe rainy season is not favorable for flea beetles. When the soil is more or less permanently moist,seedlings establish quick and are soon large enough to tolerate most flea beetle infestations. The sensitivegrowth stage is shortened and damage is reduced. Rain can also have a direct impact on flea beetles,washing them off the leaves, disturbing emergence from eggs in the soil, or destroying the larvae in thesoil by washing them away.Except for general predators like spiders, there are no specific predators or parasites that control fleaCabbage Ecological Guide - 200086

Major Cabbage Insect Pestsbeetles. Some research was done with the application of a water solution containing the nematodeNeoaplectana feltiae but no satisfactory control of the flea beetle was obtained.In Thailand, the nematode Steinernema carpocapsae is recommended by the Department of AgricultureExtension at concentration of 2000/cc. to control nymphs of flea beetle (FAO Dalat report, 1998).Management and control practicesPrevention activities:· Solarization of the nursery soil may help to reduce the number of larvae andpupae in the soil.· Healthy plants grow quickly through the susceptible seedling stage. Properseedbed preparation, or growing seedlings in pots (see section 3.7.1) and properfertilization (e.g. compost) will help to get healthy plants. See chapter 3 onagronomic practices.· Weed control is another good prevention activity as flea beetles are often associatedwith weedy areas.· Intercropping with white clover may help reducing numbers of flea beetles. Several studies show thislink. See section 3.5.3.4 on organic mulch.· Seed treatment with insecticides is becoming a common practice in many countries. Seed is(sometimes already by the seed company) covered with a thin layer of both a fungicide and aninsecticide, so that the crop is protected from seedling diseases as well as insect damage from fleabeetles. The insecticide protects the crop from moderate attacks between germination of the seedsand the first true leaf stage. If the seeds are not treated with an insecticide by the seed company,farmers can do this themselves. The advantage of seed treatment is that a relatively small quantityof insecticide is needed to obtain good protection.Seed treatment with an insecticideTake a recommended insecticide powder that is effective against flea beetle. To increase theadhesiveness of the powder, 15 ml of paraffin or vaporizing oil can be mixed with each 2 kg of seedbefore mixing the powder. Seed treated with the paraffin or oil has to be sown within a week oftreatment.Use protective gloves while handling treated seeds!Set up a field study to compare treated and untreated seed and compare the damage that mayoccur.Once flea beetles are present in the nursery/field:· Part of the adults can be trapped using sticky traps. See box below. In some areas, sticky boardsare even swept over the crop to catch adults. Some control may be achieved by sticky traps,however, large populations will not be effectively controlled.· Sometimes treating just the outside rows of a field is effective, since flea beetles migrate in fromweedy areas.87 Cabbage Ecological Guide - 2000

Major Cabbage Insect Pests· If attacks in the nursery are very heavy, additional application of insecticides can be made when theseedlings have emerged from the soil.· Crop compensation: From the transplantable stage of the seedlings (at about 5 true leaves), cabbageplants are able to compensate for most of the damage from flea beetles. Compensation capacity ofcabbage plants can be studied in trials (see also box above).· No control measures are necessary when the cabbage plants have at least 9 true leaves. Damagefrom flea beetles is usually not harmful to the plants at this stage and later.Flea beetle trapsFlea beetles can be trapped by a piece of wood coated withheavy grease. If put in the soil a few centimeters above infectedplants at regular intervals, the flea beetles will jump ontothe wood and stick to the grease.Some farmers evenused small sticky plates to sweep over the crop in orderto catch adults.¤Points to remember about flea beetles:1. Flea beetles can be a problem in nurseries and transplants, but seldom in larger plants.2. Preventive activities include solarization of the nursery soil, weedcontrol, and seed treatment.5.4 Cutworm - Agrotis sp.The name ‘cutworm’ is given to caterpillars of various moth species that feed on plants at ground level,usually cutting young plants at soil level. Most cutworms belong to the genus Agrotis. Some larvae ofSpodoptera sp. are also called cutworms although these caterpillars usually defoliate leaves.The two main species of cutworms are:· Agrotis ipsilon - black cutworm, greasy cutworm· Agrotis segetum - common cutworm, turnip mothCutworms can attack many types of vegetables and other crops including rainfed rice. They attack bothseedlings and mature crops.DescriptionLarvae are usually active during the night and spend the day hiding in the litteror in the soil. They can be found to a depth of up to 12 cm.The caterpillars have three pairs of true legs just behind the head and five pairsof false legs in the middle and last part of the body. Cutworm caterpillars curl upwhen disturbed.The larvae of the black cutworm (Agrotis ipsilon) are brown-black in color, witha pale gray band along the mid-line and dark stripes along the sides. The headis very dark with two white spots. The general appearance of the caterpillar isgreasy and black in color. A mature caterpillar is 25-35 mm long. The larvaldevelopment takes 28 - 34 days, depending on the temperature. The first twoCabbage Ecological Guide - 200088

Major Cabbage Insect Pestsinstars feed in groups on the leaves of plants, the thirdinstar becomes solitary and becomes a real cutworm(sometimes even has cannibalistic habits). The pupa ofthe black cutworm is dark red-brown and about 20 mmlong. Pupation takes 10 - 30 days depending ontemperature. Adults are large, dark moths with a wingspanof 40 - 50 mm, with a gray body. Forewings are palebrown in color with a dark brown-black pattern of markings.The hindwings are almost white but with a dark terminalline.In warm conditions, there can be 5 generations or more,depending on the temperature. Life cycle from egg toadult takes 32 days at 30 o C, 41 days at 26 o C and 67days at 20 o C.Agrotis ipsilon(Stoll, 1987)The caterpillar of the common cutworm (Agrotis segetum)is gray-brown and about 30 - 40 mm long when mature. It has faint dark lines along the sides of the body.The larval body is plump and rather greasy in appearance. The pupa is smooth shiny brown to red-brownwith two spines at the rear, about 15 - 20 mm long. Pupation takes place in the soil.Adult moths are usually smaller than the adults of the black cutworm. They measure 30 - 40 mm acrossthe wings, the forewing is gray-brown in color with a dark brown kidney-shaped marking. The hindwingsare almost white in the male but darker in the female. The body and head of the adult are brown in color.Life cycleAdult moths fly at night and can cover large distances. Female moths lay many eggs (up to 1200). Theeggs are laid singly or in small groups around the base of host plants or on leaves or stems, and onweeds or plant debris in the field. Eggs are ribbed, about 0.5 mm in diameter and pale yellow in color atfirst, later turning cream-colored to brown. The eggs of Agrotis ipsilon have reddish-yellow markings. Theeggs hatch in 3 to 25 days, depending on the temperature. At 25 o C for example, the eggs hatch in 3-4days. The first instar larvae feed on the leaves of the host plants and when larger, they go down to the soiland adopt typical cutworm feeding habits. There are usually five to six larval instars. Fully grown larvaepupate as deep as 12 cm in the soil. Pupation lasts 10 to 30 days, depending on the temperature.Cutworms can survive only where the soil is dry. Temperatures above 35 o C will kill the insects.Plant damageDamage to seedlings and young plants can be very serious. During the day, cutworms hide in the surfacelayers of the soil, under leaves or stones. At night, the larvae come to the soil surface and feed on plantstems at ground level. The stem may becompletely hollowed out just below soillevel or cut through at soil level. Typicaldamage is for the cutworm to move alongthe row of seedlings cutting each onethrough the stem at ground level. Cutwormdamage is most severe in light, sandysoils where the larvae can burrow easily.89 Cabbage Ecological Guide - 2000

Major Cabbage Insect PestsNatural enemiesThere are some parasitoids and predators of cutworms recorded, including the fly Peleterianigricornis, the nematode Hexamermis arvalis and a granulosis virus. Theentomopathogenic nematode Steinernema bibionis is being used on a commercialscale in Western countries such as the Netherlands for biological control of cutworms.The nematode Steinernema riobravis may have potential for cutworm control in thetropics.Management and control practicesGenerally, cutworms are very difficult to control because by the time infestation becomes apparent,damage may already be quite serious.Prevention activities:· Weed removal: weedy land harbors most cutworms as the adult moths prefer these sites for egglaying. Weeds also serve as food for the first instar larvae. Crops immediately following dense weedcover are therefore more likely to be seriously damaged by cutworms than crops planted in weedfreesoil.· Flooding of the infested field to drown larvae and other soil-inhabiting pests may be an option whenirrigation facilities exist. This is an option when the field is known to contain many cutworms andshould be applied before preparing the land for a new crop.· Ploughing the field will bring larvae and pupae to the soil surface for exposure to sunlight or predatorslike birds.Once cutworms are present in the field:· Hand collection of larvae may be possible for small plots. It may not be practical for cabbage productionon larger scale. The cutworms can be found in the soil near plants attacked. Cutworms may also betrapped under small pieces of wood or pieces of rigid cardboard, placed in the field. When searchingfor shelter during the day, the cutworms may hide under these things and can be collected moreeasily.· Irrigation during dry periods may help to control cutworms because moisture in the soil reduceslarval survival.· Chemical control is usually not effective: the soil-dwelling stages of the cutworms, often under denseand continuous crop foliage make them difficult to “hit” with insecticides. For this reason, sprays arevery often not effective against cutworms. Most sprays are targeted against the first instars that feedon the plant leaves, timing is very difficult and often again, the sprays are not effective.· Cutworms can sometimes be controlled with baits containing an insecticide mixed with moistenedbran or vegetable pulp and spread over infested areas or placed under covers to retain moisture.Chopped cabbage leaves mixed with an insecticide can be spread between the cabbage rows asbait. Check with local extensionists if there is any experience with using baits for cutworm controland, if so, when and how they should be applied. Set up a small trial in your field to test if the baitsare effective.· Where available, biocontrol agents such as entomopathogenic nematodes may be an option.Cabbage Ecological Guide - 200090

Major Cabbage Insect Pests¤Points to remember about cutworms:1. Cutworms can be a problem in nurseries.2. No effective biocontrol agents are available to date although the option of cutworm managementwith entopathogenic nematodes needs further study3. Weeding might prevent cutworm infestation.4. Use of baits can be an effective cutworm control measure.5.5 Armyworm - Spodoptera sp.The name ‘armyworm’ is the common name for a stagein the life cycle of certain moths. Most of them belong tothe genus Spodoptera but there are other caterpillars thatmay be classified as armyworms. “Armyworm” is more abehavioral term: when the supply of food for armywormsis running out, they may “march off” over the ground likean army to find new feeding locations. With very largepopulations, the ground may be completely covered with“marching bands” of caterpillars.Spodoptera lituralisThis behavior however, depends on the circumstances. For example, Spodoptera litura/littoralis in smallnumbers feed on the leaves of plants but will sometimes act as a cutworm (in rice) and at other times willswarm in groups and act as a typical armyworm.Armyworms attack many crops including cotton, tomato, rice, tobacco, maize, legumes and many othercrops.The main species of armyworms of importance for vegetables are:· Spodoptera exigua - lesser armyworm, beet armyworm· Spodoptera lituralis - common cutworm· Spodoptera litura (= Prodenia litura) - fall armyworm, cluster caterpillar, rice cutworm, cotton leafwormSpodoptera lituralis andSpodoptera litura haveonly recently beenseparated as differentspecies by the genitaliaof the adult moths. OneSpodoptera lituralisneeds a very good lensto be able to see theSpodoptera lituraSpodoptera exiguadifference. Thecaterpillars of the twoare not really separableas caterpillars of allarmyworms can havedifferent colors fromgreen to black, andchange this colour according to host plant tissue eaten. However, it is important to be able to separatethem into the right species. This is because effective NPV has been developed as biocontrol agent. NPVis very specific to the species and applying the “wrong” NPV will not give effective control.91 Cabbage Ecological Guide - 2000

Major Cabbage Insect PestsDescription and life cycleAdults of armyworms are gray to gray-brown in appearance, with a wingspan of about 25 mm. Theforewings are yellow-brown with white and black patterns. The hindwings are whitish. They do not usuallyfly far and lay their eggs close to the place of emergence. Eggs are laid in large masses on the undersidesof host plant leaves. Each egg mass has a fuzzy appearance because it is covered in fine hairs andscales from the body of the female. About 500 - 2000 eggs per female are deposited in batches of 50 -200 over a few days period. The eggs are ribbed, and range in color from green-gray when freshly laid,becoming very dark in color just before hatching.Egg hatch occurs 2 - 6 days after laying. Caterpillars of armyworms feed in groups together for a whilebut spread out when they become older. They usually feed at night.Newly hatched caterpillars are light green in color and about 1 mm in length with relatively large heads.They undergo five or six moults and reach a length of 35 - 50 mm before burrowing into the soil forpupation. When fully grown, caterpillars vary in color from light tan or green to almost black. Larvae of S.exigua are often green in color with a white line along the side; S. littoralis are often brown to black andcan have more black spots/stripes on the body. They are also usually a bit larger than S. exigua. Larvaeof S. litura and S. littoralis have a distinct black band on the first abdominal segment. The head is black.They feed together in groups. The pupa is dark red in color, 15 - 20 mm long. The pupal stage takes about12 days.Plant damageArmyworms skeletonize host plant leaves. Egg batches are laid closetogether and in a severe year clusters of many caterpillars may rapidlydefoliate of cabbage plants. This is usually a problem from seedlinguntil cupping stage. When the cabbage head is formed, usually notmuch damage is done.Natural enemiesGood results have been achieved with the use of nuclear polyhedrosis viruses (NPV) for the control ofarmyworms. These NPVs have become an important biocontrol agent in IPM systems. There are differentstrains of the NPV:SlNPV for control of Spodoptera lituraSeNPV for control of Spodoptera exiguaNPV is being tested at various locations in Asia, e.g. Vietnam, Philippines and Indonesia. Some countriesare already using it on large scale.Cabbage Ecological Guide - 200092

Major Cabbage Insect PestsSome NPV study data from VietnamA vegetable FFS-graduate farmer group in Ha Tay village, near Hanoi, started experiments with theuse of NPV against Helicoverpa and Spodoptera on cabbage and tomato. The group did both pottingexperiments and field studies with NPV which was supplied by the National Institute of Plant Protection.Some of the conclusions that were drawn from their potting experiments :· Larvae that die from NPV change color from green to yellow, they diesslowly (several days), the skin breaks easily, then fluid comes out,and the caterpillar may hang down from the leaves.· Small larvae are more susceptible than larger sized larvae. Mortalityrates were 100% for small, 90% for medium and 85,5% for large sizedlarvae. The group concluded NPV should be applied to the field whenlarvae are still small.· NPV did not have any effect on natural enemies in jar experiments.· Larvae infected with NPV die within 3 to 4 days.· NPV-infected larvae eat less (area of leaf) than healthy larvae.· In jars, NPV was still viable after 2 days but this may not be the casein field where there is sunshine, rain, etc.In a field study, the farmer group found that NPV gave 80% control of armyworm.The farmers concluded that NPV is better than chemical pesticides because it gives equal or bettercontrol of the specific pests. In addition, it may spread through populations in the field. However, theyalso recognized that the effect of NPV is short (break-down by sunlight) so it needs to be appliedmore often. On-farm production of NPV has not been tried so far by this group (pers. comm. Ha Tayfarmer group, April 2000).In Indonesia, the Biological Control Research Center (of the National Institute of Plant Protection, Indonesia)has developed a method of production and application of NPV, which can be done by farmers. Usually,starter cultures of NPV are supplied by institutes such as the National Institute of Plant Protection. Seesection 6.3.3 for NPV production guidelines and some quality matter.Other natural enemies:Preparations of Bacillus thuringiensis (Bt) have been found to be effective against armyworms.In Lao PDR, the larval parasitoid Microplitis sp. was found parasitizing Spodoptera in cabbage andcauliflower (pers. comm. A.Westendorp, 2000).Management and control practicesPrevention activities:· Burning of crop stubble and removal of weeds help to lower the pest population. The armyworms maysurvive on crop stubble and weeds after harvest and infest a newly transplanted crop, causing cropinjury.· Flooding of the infested field to drown pupae and other soil-inhabiting pests may be an option whenirrigation facilities exist. This should be done before preparing the land for a new crop.· Ploughing the field will bring larvae and pupae to the soil surface for exposure to sunlight or predatorslike birds.93 Cabbage Ecological Guide - 2000

Major Cabbage Insect Pests· In some cases, armyworms may be more attracted to trap crops rather than cabbage. It might beworth trying a few crops to see if the armyworm population is larger on the trap crop than on thecabbages. A potential trap crop may be sunflower. These were promising when used as trap crop forgroundnut.Once armyworms are present in the field:· Hand collection of larvae and egg masses may be possible for smallplots. It is not practical for cabbage production on larger scale..· The biocontrol agent NPV is becoming increasingly available in manycountries in Asia. The NPV is quite specific for a host insect andsymptoms are easily recognized in the field. In addition, NPV are easilyproduced, applied and evaluated by farmers. See also section 6.3.3 onCollecting insectsby handNPV. In Indonesia for example, application of SeNPV along with hand picking larvae provided thebest control of S.exigua in shallot fields. The highest yields were obtained in the treatment whereSeNPV was carried out with hand picking (Shepard, 2000). See box in section 6.3.3.· Availability of biocontrol agents has made insecticides for control of armyworms redundant. WhereNPV is not available, and a pesticide application is considered, balance benefits from pesticideapplication against harm done to natural enemy population. Spraying for armyworm may result inmore trouble with e.g. DBM because their natural enemies are killed!¤Points to remember about armyworm:1. Yield loss from armyworm damage in cabbage is usually not severe.2. Very effective biocontrol agent NPV is available in many countries.3. Chemical control of armyworm is usually not necessary.Related exercises from CABI Bioscience/FAO manual4-A.3. Plant compensation study4-A.9. Hand picking of eggs and caterpillars5.6 Cabbage heart caterpillar - Crocidolomia binotalisSee illustration Plate 1 Fig. 1This insect has become an important secondary pest in some areas,for example in Indonesia.Another name used for this insect is the webworm, cabbage headcaterpillar or cabbage leaf-webber. There seems to be some confusionwith the name “webworm” being either Crocidolomia binotalis or Hellula undalis. See section 5.7 below.Description and life cycleThese slightly hairy, small (15 - 25 mm) caterpillars have orange heads, a creamy-yellow underside anda light green back with fine, longitudinal white lines. They are easily recognized by their distinctiveyellowish white stripes: three dorsal and two lateral. These stripes disappear only when larvae are closeto pupation. The sides of the body are brownish with black spots. Up to 50 caterpillars may be foundgrouped together in a network of threads on a single cabbage.Cabbage Ecological Guide - 200094

Major Cabbage Insect PestsAdults are active at dawn and at night. Adult females can live as long as 30 days and lay as many as 10or more egg clusters for an average total of 350 eggs. Eggs are laid in batches of up to one hundred.These are flattened and are packed neatly like roof tiles on young cabbage leaves. Egg masses are lightgreen in color and are usually laid on the underside near the base of leaves.The caterpillars hatch in about 4 days. The caterpillar stage may take about 12 days with a total of fivemoults. Larvae burrow into the soil near the base of the host plant to pupate. They weave a loose cocoonwhich they cover with bits of available substrate, usually soil. This make pupa difficult to find.The Crocidolomia life cycle is completed in approximately 28 days, depending on temperature andhumidity. They are almost exclusively found in hot humid highland tropics. They are a more serious pestproblem during the dry season since heavy rains can drown small larvae.Plant damage and plant compensationLarge numbers of caterpillars are feeding together on a single plant. For the first 4 or 5 days fromhatching, the small larvae feed on the underside of the leaf without eating through the upper leaf layer,creating window-like damage in the leaves. After this they move to the growing point of the plant centeror bore to the center of the head. In the open center, groups of caterpillars will conceal themselvesbeneath silk webbing and frass. Crocidolomia damage results in a completely destroyed plant or falsecabbage head with no real head or several small heads.Larvae are very mobile and can easily travel 2 or more meters to reach a preferred host plant. Also, assoon as larvae have begun boring into a cabbage head they are protected from contact with insecticidesor biocontrol agents.Natural enemiesBacillus thuringiensis (Bt) works for Crocidolomia caterpillar control.Two fungi, Nomuraea rileyi, and Erynia sp. have been found killing webworm larvae in Indonesia (FAO-ICPProgress report ‘96 – ’99; Shepard et al, 1999). Methods for production and distribution are beinginvestigated. See section 6.3.2 on fungi as natural enemies.Several Hymenopteran larval parasitoids have been identified for Crocidolomia. In the Philippines, thelarval/pupal parasitoid Aulacocentrum philippines (Braconidae, Hymenoptera) is being studied for controlof Crocidolomia binotalis. A field study by the Department of Entomology/UPLB in Quezon Province in1996 showed 59% parasitism (pers. Comm. Dr. Belen Rejesus, July 2000).There may be potential for entomopathogenic nematodes as biocontrol agents. Further studies areneeded.Management and control practicesPrevention activities :· It is preferable to plant cabbage during the rainy season when populations are reduced. However,cabbage crops in the rainy season may have more disease problems.· Trap cropping: Crocidolomia caterpillars prefer mustard plants to cabbages. That means there is apotential for planting mustard as a trap crop. In India for example, 15 rows of cabbage were successfullyintercropped with Indian Mustard (planted 12 days prior and 25 days post cabbage transplant). Seealso section 3.10.95 Cabbage Ecological Guide - 2000

Major Cabbage Insect Pests· Ploughing field to will expose pupae to drying sun and birds.· Removing plant debris after harvest and before transplanting to reduce populations.Once the Crocidolomia caterpillar is present in the field:· Hand removal of egg masses and early instars: trials done reflect that handpicking of caterpillars isa good way of control. During the first 40 days after cabbage transplant, while leaves are still openand relatively few, caterpillars are easy to spot in the field. The first symptoms are “windows” in theleaf. Handpicking was easier and quicker than spraying individual plants with an insecticides becausefor good chemical control, the whole plant needs to be sprayed very thoroughly. At a later croppingstage, removing infested plants and destroying them is an effective control measure. Regularhandpicking of egg masses in combination with Bt applications has also been found effective inreducing damage (Shepard et al, 1999)· Preparations of Bacillus thuringiensis (Bt) can be effective against this caterpillar. Spot spraying onlythose cabbage plants with visible Crocidolomia caterpillars is an effective means of control. Whencabbage plants enter cupping stage, Crocidolomia caterpillars become more difficult to detect. Inareas with high populations, it may be an option to spray Bt regularly when damage is seen. However,once larvae are inside cabbage heads, Bt are no longer effective.· Spraying chemical pesticides is not recommended. Most pesticides are no longer effective whenlarvae begin boring into the cabbage heads where they are inaccessible. Pesticide application cannotbe considered in isolation from other pests such as diamondback moth. Spraying against Crocidolomiadecimates the natural enemy population that may control DBM (e.g. D. semiclausum).¤Points to remember about cabbage heart caterpillar:1. Crocidolomia caterpillars can locally be a serious pest.2. Handpicking egg masses and early instars during early growth stages is a good way of control.3. Destroying infested plants is valuable after cupping stage to prevent further damage.4. Spot applications of Bt can work against caterpillars but only before the cupping stage.5. When caterpillars have bored inside cabbage heads, Bt and chemical pesticides are usually noteffective.5.7 Cabbage webworm - Hellula undalisSee illustration plate 1 Fig. 2This insect is also called cabbage borer and oriental cabbage webworm.There seems to be some confusion with the name “webworm” being eitherCrocidolomia binotalis or Hellula undalis. See section 5.6 above.Description and life cycleEggs are laid singly or in a row on cabbage plants.The larvae of this insect have a length of about 15 mm and they are pale cream to green or gray in color.The head is dark brown to black. The body has several narrow dark stripes along the back and sides ofthe body. The larvae mine the leaf midribs or feed inside the cabbage heart under protective silken webs.Pupation occurs inside a cocoon made of soil just below the soil surface.Cabbage Ecological Guide - 200096

Major Cabbage Insect PestsThe adult moth is small (up to 9 mm) with light brown wings.The life cycle extends to about 4 weeks, depending on the temperature.Plant damage and plant compensationThe main damage is caused to young seedlings and to young cabbage transplants, unlike Crocidolomiacaterpillars which can affect cabbage plants at any stage. On hatching from the egg, the young Hellulalarvae bore into the base of the leaf-midribs, and also into the stem, sometimes going down as far as theroots before emerging for pupation. Seedlings may be attacked by several larvae at the same time, andeither die or develop into poor feeble plants. Cabbages often develop small, multiple distorted heads of nocommercial value. Nurseries can be totally destroyed in a few days.Webworm attack can be particularly high during and immediately after the wet season. High temperaturesand high humidity, such as would occur during and just after the rainy season, favor the development ofthis insect. The critical period begins when the first true leaves are forming.This insect of often considered a serious pest in lowland crucifers, but is less serious in highland areas.Natural enemiesPreparations of Bacillus thuringiensis (Bt) may be effective but only before larvae have bored into stemsor cabbage heads, and before they are protected by silken webs.Management and control practicesPrevention activities:· Burning of crop stubble and removal of weeds help to lower the pest population. Some webwormsmay survive on crop stubble and weeds after harvest and infest a newly transplanted crop, causingserious crop injury.· The critical period for webworm attack begins when the first true leaves are forming. It is important toinspect the nursery every few days for presence of these caterpillars, especially during or shortlyafter the rainy season.Once the webworm is present in the field:· Low populations in the nursery may still be controlled by handpicking the caterpillars or eggs.· Removal of infested leaves or even the growing point may be considered. The cabbage plant willcompensate for the loss of leaves and even the loss of the main shoot by producing new leaves andshoots. All but one shoot will have to be removed. See section 4.5 on plant compensation.· Larger populations in the nursery or in the field may be controlled by a spot application of Bt or a(systemic) insecticide. Spot applications minimize the use of biological or chemical insecticidesand may save at least part of the beneficial insect species. Bt applications can work against webwormbut need to be applied before caterpillars are protected inside the leaf or under webbing.97 Cabbage Ecological Guide - 2000

Major Cabbage Insect Pests¤Points to remember about webworm:1. Webworm caterpillars can locally be a serious pest, especially of nurseries and young transplants.2. Handpicking of caterpillars helps to prevent population build-up.3. Removing infested leaves or the main bud may be considered. The cabbage plant will compensateby producing more leaves and shoots.4. Bt applications can work against caterpillars but need to be applied before caterpillars areprotected inside the leaf or under webbing.Related exercises from CABI Bioscience/FAO manual:4-A.94-A.104.A.13Handpicking of eggs and caterpillarsIntegrated management of webworm on cabbageComparison of biological and chemical pesticides used in caterpillar control5.8 Cabbage looper - Trichoplusia niThere are several English names for this insect: cabbage looper, cabbage semilooper, ni moth or thefalse cabbage looper.DescriptionThe adult looper is a dark brownish moth with two small white markings on the forewings, sometimesresembling the figure “8”. Wingspan is about 35 mm. Adults live for about 3 weeks.The moths are night fliers, but can be seen during the day resting on the underside of cabbage leaves.The cabbage looper is a smooth yellow-green caterpillar with a whitish line down each side, and theforepart of the body slightly narrower than the rest. It can have two white lines along the middle of theback. Fully grown caterpillars measure 30 - 35 mm. There are two pairs of prolegs so a caterpillar walksby arching its body as a “looping” action which is characteristic for this insect. The caterpillars first eat onthe leaf borders but as they mature, they move deeper into the cabbage heads.The main host plant for the semi-looper are cruciferous crops but it can also feed on cotton, legumes,solanaceous crops like potato and tomato, sweet potato, some cucurbits and many other vegetables.Trichoplusia ni adult moth “looping” caterpillar PupaLife cycleEggs are laid singly on the underside of the lowest leaves, and hatch in about 2 - 3 days. Each femalecan lay up to 200 eggs. The eggs are white to yellow in color, round, about 0.5 mm in diameter and hatchin 2 to 3 days. The eggs are not securely glued to the leaf and can be brushed off easily.Cabbage Ecological Guide - 200098

Major Cabbage Insect PestsLarval development takes some 30 to 35 days. There usually are five instars.Pupation takes place in a silken cocoon, usually in the leaf litter or crop debris. In cabbages, the cocoonmay also be in the heart of the plant between leaves. The pupa is brown and about 20 mm long. Underoptimum conditions, development of the adult inside the cocoon takes about 15 days.In (sub)tropical areas there may be 5 generations per year or more as a result of continuous breeding.Even in temperate areas, the caterpillars continue to be active at low temperatures.Plant damageThe caterpillars of the semilooper eat large, irregular holes in the leaves. Young larvae skeletonize leaves,the older larvae eat the entire leaves, sometimes causing plant defoliation. As loopers mature, they movedeeper into the cabbage heads. They can consume large parts of the hearts of cabbages, and contaminatingit with frass. Plant development may be retarded and the quality of cabbages will go down.Compared to other caterpillars, cabbage loopers are not very destructive. Although one looper larvaedoes approximately three times the damage of one Pieris rapae larva and can consume almost 20 timesas much foliage as a diamondback moth larvae, their numbers are less and they do not eat deep in theheart of the cabbage.There are pheromones available for looper monitoring.Natural enemiesMany natural enemies are recorded for this species and natural field mortality may sometimes be high.Nuclear Polyhedrosis Virus (NPV) and Bacillus thuringiensis (Bt) are effective against this pest. However,some trials report that Bt is less effective against the cabbage looper.During the wet season, some fungus species may attack and kill the cabbage looper.Management and control practicesPrevention activities:· Removing or burning of crop residues and removal of weeds help to lower the pest population.Cabbage loopers may survive on crop stubble and weeds after harvest and infest a newly transplantedcrop, causing new crop injury.· Ploughing the field may bury crop residues containing looper pupae in the soil where they die.Once cabbage loopers are present in the field:· Hand collection of larvae may be possible for small plots. It may not be practical for cabbageproduction on larger scale.· Biological control with preparations of Bacillus thuringiensis (Bt) may be effective. Bt is mostlikely to be effective on young, active looper larvae exposed during time of application.· Chemical control has been difficult to achieve as the cabbage looper has developed resistance tomany insecticides including carbaryl, parathion, methomyl and others.99 Cabbage Ecological Guide - 2000

Major Cabbage Insect Pests¤Points to remember about cabbage loopers:1. Cabbage loopers are seldom a serious pest in cabbage.2. Cabbage loopers have many natural enemies in the field.3. Chemical control for loopers is usually not effective.5.9 Cabbage white butterfly - Pieris rapae and Pieris brassicaeBoth Pieris rapae and Pieris brassicae are widespread pest insects of crucifer crops in Asia, mostly inthe cooler region or highlands. Pieris rapae seems to be more important than Pieris brassicae in Asia.DescriptionThe adults of Pieris rapae have whitewings and the forewings have black tips.Females have two black spots in themiddle of each forewing. These spotsmay also appear grayish in color. Themale has one black spot in the middleof each forewing, although occasionallythe wings may be pure white withoutdark spots on the tips. The hindwingsare all white on the surface except for ablack spot on the outer front margin.Pieris brassicae(from: Stoll ‘87)Pieris rapae adult(from: www21)Adults of Pieris brassicae look much like Pieris rapae but they are slightly larger with a wingspan of 50- 70 mm. The wings are white in color with black tips on the forewings. In addition to these black tips, thefemale has two large black spots on the upper surface of each forewing.Caterpillars of Pieris rapae have a green velvet appearance, with faint yellow lines down the back andyellow patches along their sides. When fully grown, they are about 25 -30 mm long.Pieris rapae usually pupates on the plants although pupae can be found on sheds and walls. They restvertically on a pad of silk to which it is attached by a silken girdle. The pupa usually color-match thesurroundings: pupae found on actively growing plants are deep green whereas pupae found on dead plantmaterial are usually dull gray and speckled to match the background. Completion of the pupal stageranges from one to two weeks.larva of Pieris rapae(from www11)Pieris brassicae caterpillar(from: Kirk, 1992)Caterpillar of Pieris brassicae are pale green in color at first, but they rapidly become mottled blue-green,with many black markings. When fully grown, each caterpillar is 25-40 mm long and has three yellowcoloredlines down the back, and yellow along the sides of the body. Each has groups of short, stiff, whitehairs along the body. Caterpillars tend to stay together in small groups.Cabbage Ecological Guide - 2000100

Major Cabbage Insect PestsLife cycleLife cycles of Pieris rapae and Pieris brassicae are slightly different, and are described separately below.Pieris brassicae :The females lay their yellow, flask-shaped eggs in batches of 20 to 100 on a cruciferous plant, usually onthe underside of leaves. The eggs hatch in about 14 days and the young caterpillars first eat theireggshells and then feed on the leaves. They stay together in a small colony. After the third moult, thecaterpillars disperse, many moving onto new leaves. Usually, most of the caterpillars feed on only oneplant. They are easily seen feeding on both surfaces of the leaf. When populations are large it is commonto see plants completely defoliated with just leaf stalks and some midribs remaining. After feeding forabout 30 days, the caterpillars leave the host plant and search for sheltered pupation sites on vertical oroverhanging surfaces on trees, walls, fences or similar objects. Each larva spins a silken pad to which itattaches itself in an upright position. It then makes a silken girdle around its waist to hold it in position.The pupa is gray-green in color with yellow and black marks. After about 15 days, the adults emerge.Their wings are crumpled at first but within hours they expand and dry.Pieris rapae :Eggs are often laid on many different plants within a field. The eggs are laid individually on the undersideof leaves. The pale-yellow colored, bottle-shaped eggs hatch in about 3-15 days, depending on thetemperature. Caterpillars feed solitary, usually in the heart or around the growing point of the plant. Laterinstars rest openly along the mid-ribs of the leaves. Although dark green in appearance, the presence ofthe larvae is easy to find by the damaged leaves with accompanying frass.Plant damage and plant compensationThe caterpillars eat the leaves and defoliate the plants and contaminate them with large quantities offeces. In heavy infestations leaves are reduced to the midribs and the plants are killed. The larvae feed onthe first formed outer leaves of their host plants, which often appear riddled with irregularly shaped holes.As the caterpillars become mature, they feed in the center of the plant. Their excretions can be foundbetween the leaves.Caterpillars of Pieris rapae are feeding more solitary than larvae of Pieris brassicae so individual plantdamage is usually less severe but more plants may be damaged.Pieris species are sometimes considered to be a pest, not because of the amount of crop it destroys,but because of the amount of frass contamination which can make cabbages of a lower quality grade.The frass is particularly troublesome in cabbage crops near harvest as the pungent-smelling frass islocated between the wrapper leaves and the cabbage head.Natural enemiesPieris larvae are commonly parasitized by a wasp, Cotesia(Apanteles) glomerata, and pupae by another wasp, Pteromaluspuparum. Meteorus versicolor is also reported as natural enemy ofPieris rapae. Often, natural occurrence of these parasitoids makesadditional control unnecessary. In fact, control action can bedamaging as insecticides can easily kill parasitoids, resulting inmore damage from the caterpillars.CotesiaThe parasitoid Cotesia (Apanteles) glomerata can achieve very effective control of caterpillars. The small,bright-yellow colored cocoons of Cotesia glomerata can be seen alongside the dead and dying caterpillar101 Cabbage Ecological Guide - 2000

Major Cabbage Insect Pestsfrom which the parasitoids have emerged. See also section 6.2.3 for details on Cotesia glomerata. InVietnam, this parasitoid has been brought to Dalat, a highland area, for Pieris control (FAO-ICP progressreport ’96 – ’99). The Hung Yen rearing unit in the area is establishing mass-production facilities for thenatural enemy Cotesia glomerata. Once this has been established, field releases combined with farmertraining will be set up (FAO Dalat report, 1998).Commercial preparations of Bacillus thuringiensis (Bt) are available as biological insecticides and areeffective in some areas but not in others. In Dalat, south Vietnam, for example, farmers reported that Btwas not effective against Pieris. This is why the parasitoid Cotesia glomerata was imported.A Granulosis Virus (GV) can be an important mortality factor. This GV can possibly spread through theparasitoid Cotesia (ref. www16). See sections 6.2.3 and 6.3.3.Chickens and ducks like to eat these caterpillars when they roam around in the field. Often however, theyonly eat the caterpillars that have dropped on the ground. They are therefore not very effective in controllingthese caterpillars but do contribute a little. Caterpillars are also eaten by some other birds and predatoryground beetles.Management and control practicesPrevention activities:· Some prevention is obtained when crop residues are removed from the field after harvest. Theseresidues may be sources of infestation when they contain eggs or young larvae. The larvae caneasily spread to the new crop. The crop residues can be buried into the soil, fed to farm animals,added to a compost pile or collected, dried slightly and burnt. Removing crop left-overs is also veryvaluable for prevention of other insect pests and diseases.Once the cabbage white butterfly is present in the field:· Hand-picking of egg masses and young larvae is recommended when cabbage is grown in smallplots. Also when only a few plants are attacked, handpicking of caterpillars is useful. Effectivecontrol can be achieved with this.· Monitor field for signs of natural control by parasitoids. Natural control percentages can be very highand no additional chemical control is necessary in that case.· Chemical control of this caterpillar with insecticides is difficult because once the caterpillars haveentered the hearts of cabbage plants, they are protected by leaves and sprays are not effective.Consider spot applications when insecticide spray is still found necessary.· When large numbers of caterpillars are attacking many plants in the field, consider applying apreparation of Bacillus thuringiensis (Bt). Efficacy of Bt preparations may also be tested in insectzoos before applying to main field. See section 6.3.1.¤Points to remember about Pieris species:1. Pieris species can be a problem in cabbage fields because caterpillars defoliate plants, andcontaminate the crop with frass, which can make cabbages of a lower quality2. Where available, the parasitoid Cotesia glomerata can give effective control of Pieris larvae,when pesticides are not used.3. Bt spray may be effective for Pieris sp.control.Cabbage Ecological Guide - 2000102

Major Cabbage Insect Pests5.10 Whitefly – Bemisia tabaciBemisia tabaci is a very common species of whitefly. However, there are several other species, forexample Aleurodicus dispersus (spiraling whitefly), and Trialeurodes vaporariorum (common whitefly).Other English names: tobacco whitefly, cotton whitefly or sweet potato whitefly.White fly currently is known to attack over 500 species of plants representing 74 plant families. Theyhave been a particular problem on members of the squash family (squash, melons, cucumbers, pumpkins),tomato family (tomato, eggplant, potato), cotton family (cotton, okra, hibiscus), bean family (beans,soybean, peanuts), and many ornamental plants.In Cebu, in the Philippines, serious damage on cabbages by the whitefly Bemisia tabaci occurred duringthe dry season. Injudicious use of pesticides and favorable temperature led to whitefly outbreak in thearea (Ref. FAO-ICP progress report April 1996 – Feb 1999).Description and life cycleThe adult whitefly is very small: about 1 mm long, silvery-white in color and with wings of a waxy texture.It is found often on the underside of the foliage where it sucks the plant sap.When a plant containing whiteflies is shaken, a cloud of tiny flies flutter out but rapidly resettle. The adulthas 4 wings and is covered with a white, waxy bloom. Adults can fly for only short distances but may bedispersed over large areas by wind. Females usually lay their first eggs on the lower surface of the leaf onwhich they emerged, but soon move upwards to young leaves. The female may lay 100 or more eggs.The egg is pear-shaped and about 0.2 mm long. It stands upright on the leaf. The eggs are anchored bya stalk which penetrates the leaf through a small hole made by the female. Water can pass from the leafinto the egg, and during dry periods when there are high numbers of eggs, the plant may become waterstressed.Eggs are white when first laid but later turn brown. Early in the season, eggs are laid singly butlater they are laid in groups. They hatch in about 7 days.When the nymphs hatch they only move a very short distance before settling down again and starting tofeed. Once a feeding site is selected the nymphs do not move. All the nymphal instars are greenishwhite,oval and scale-like. The last instar (the so-called “pupa”) is about 0.7 mm long and the red eyes of1. Egg (actual size about 0.24 mm long)2. & 3. Top and side view of 1 st stage nymph4. 4 th stage nymph (actual size about 0.75 mm long)adult whitefly(from Kerruishet al. 1994)103 Cabbage Ecological Guide - 2000

Major Cabbage Insect Peststhe adult can be seen through its transparent back. The total nymphal period lasts 2 - 4 weeks dependingon temperature. Nymphs complete 3 moults before pupation.Eggs and early instar nymphs are found on the young leaves and larger nymphs are usually morenumerous on older leaves.Attacks are common during the dry season. Whiteflies disappear rapidly with the onset of rain.Plant damage and plant compensationDirect crop damage occurs when whiteflies suck juices from the plant. With high populations plants maywilt, turn yellow and die.Colony of white flies on underside of leaf (from Stoll ‘87)Whiteflies also excrete honeydew, a sweet sticky fluid which may cover the leaves completely. On thishoneydew, mould fungi grow and the leaves may turn black in color. This reduces the capability of theleaves to produce energy from (sun)light (photosynthesis) and may lower harvest quality.In some hosts, damage can result from whitefly feeding toxins that cause plant disorders such as silverleaf of squash and irregular ripening of tomato. Plant viruses also can be transmitted by whiteflies, but forcabbage this is not a serious problem.Natural enemiesWhiteflies are controlled by predatory insects such as green lacewing or coccinellid larvae (lady beetles);by parasitic wasps such as Encarsia or Eretmocerus species; and fungal diseases such as Beauveria,Paecilomyces or Verticillium species.There may be many more natural enemies of whitefly in your area!Natural enemies of whitefly, to name but a few….Studies carried out between 1985 and 1987 in Andhra Pradesh, India, on cotton showed theoccurrence of nymphal parasitism of whitefly due to the aphelinids Eretmocerus serius, Eretmocerussp. and an unidentified aphelinid. Populations of predators included the coccinellids Brumoidessuturalis, Verania vincta, Menochilus sexmaculatus, Chrysoperla carnea, and the phytoseiidAmblyseius sp. Fungal pathogens found included Aspergillus sp., Paecilomyces sp. and Fusariumsp. (Natarajan, 1990)Cabbage Ecological Guide - 2000104

Major Cabbage Insect PestsParasitic wasps usually are more effective at low pest population densities, whereas predators are moreeffective at high population densities. Parasitism can be quantified by counting the number of emptywhitefly pupal cases with a circular exit hole (created by the emerging adult wasp) rather than a “T”shaped split (created by the normal adult whitefly emergence).In Cebu, the Philippines, field parasitism of whitefly by the parasitoid Encarsia sp. ranged from 75 to90%! (Ref. FAO-ICP progress report April 1996 – Feb 1999).Numbers and activity of whitefly parasites and predators can be encouraged by avoiding broad-spectruminsecticides, planting of refuge crops, and -in some areas- augmentative releases.Whitefly mortality from pathogenic fungi often reach high levels in greenhouses where relative humidity isconstantly high and spores naturally accumulate. Pathogenic fungi can be applied as a spray treatmentand are effective at any population density. Insect pathogens used for whitefly control must be appliedwith good coverage and under proper environmental conditions (high relative humidity) to be effective. Thefungus Verticillium lecanii is commercially available in Europe for the control of greenhouse whitefly.Other products are being tested in commercial production fields and greenhouses, but the economicfeasibility of their use has yet to be determined.Another fungus called Paecilomyces fumosoroseus is also commercially available for whitefly control. Itcan be applied as a spore solution and it has some activity against aphids, thrips and spider mites. InCebu, Philippines, Paecilomyces sp. was found native in the field (Ref. FAO-ICP progress report April1996 – Feb 1999).Management and control practicesWhitefly management in a crop will depend greatly on the severity of damage caused in that crop and thenumber of whiteflies required to cause this damage. Very few whiteflies are required to transmit viruses,so where this is the major concern, a farmer will want to avoid even small numbers of whiteflies. Wherelow levels of whiteflies are tolerable, which is the case in most cabbage growing areas, other methodssuch as biological control can be more effective.Prevention activities:· Plant resistant cabbage varieties where available. Check local seed supplier in areas where whiteflyis a serious problem.· Proper monitoring of the whitefly population should be done regularly to detect early infestation. Theeasiest method of monitoring for whiteflies is leaf inspection. Sampling 100 leaves per field (one leafon each of 100 randomly selected plants) can provide a very good estimate of the average whiteflypopulation density in the field, but fewer samples are usually all that is needed to make a controldecision.· The movement of whitefly adults can be monitored with yellow sticky traps. This method can providea relative measure of general population trends over an extended area. In China for example, thesetraps are widely used in both greenhouses and in the open field. Careful monitoring of the types andnumbers of insects caught on the traps should be done as yellow traps may also attract largenumbers of useful natural enemies! When this happens, the traps are better removed from the field.· Destroy old crop residues that harbor whitefly infestations unless large numbers of natural enemiesof whitefly are detected.· Susceptible crops should not be grown continuously because whitefly populations expand rapidly ifthere is a continuous supply of food.105 Cabbage Ecological Guide - 2000

Major Cabbage Insect Pests· Avoid planting next to crops infested with whitefly and avoid carry-over from infested plant material.· To protect seedlings, insect netting or screen cages of very fine wire mesh, placed over nurseries,helps reducing initial whitefly infestation of young plants.· Under field conditions, there are several types of barriers that can reduce whitefly problems. Theseinclude reflective mulches that tend to repel whiteflies, oil-coated yellow mulches that act as a trapfor whiteflies, floating row covers (generally made out of a light fiber mesh and placed over newlyplanted crops) that exclude whiteflies during the vegetative growth of the crop, and trap crops.· Planting time also can be an effective tool to avoid whiteflies because they reproduce more rapidlyunder hot, dry conditions. Thus, planting during or shortly after rainy season allows crops to beestablished and even mature before conditions are favorable for rapid population increases.· Establishing a host-free period by careful choice of planting site and date can reduce whiteflypopulations. This practice requires regional cooperation to be effective.· Avoid unnecessary applications of pesticides to prevent secondary outbreak of whiteflies (due toelimination of natural enemies).4Spraying insecticides resulting in MORE whiteflies??!!There is a possibility that treating a resistant whitefly population with certain insecticides couldactually accelerate population growth. This could be because more eggs are laid when the insect isunder biochemical stress, or because natural enemies are eliminated.To minimize this potential problem, insecticide applications should be used as little as possible,judiciously and combined with non-chemical control techniques.Once whiteflies are present in the field:· Chemical control of whiteflies is both expensive and increasingly difficult. Many systemic and contactinsecticides have been tested for control of whiteflies, but few give effective control. Besides thecost of treatment, other factors involved in chemical control decisions are:· the need for thorough coverage: whiteflies are located on the undersides of leaves where they areprotected from overhead applications, and the immature stages (except for the first one) areimmobile and do not increase their exposure to insecticides by moving around the plant,· the risk of secondary pest outbreaks (due to elimination of natural enemies),· the risk of whiteflies developing insecticide resistance (a very serious threat!), and· the regulatory restrictions on the use of insecticides.¤Points to remember about whitefly:1. Whitefly populations in cabbage can be high, but infestation seldom leads to severe crop losses.2. Whitefly has many natural enemies which can keep populations low.3. Avoid unnecessary application of pesticides to prevent secondary outbreak of whiteflies due toelimination of natural enemies. Treating pesticide-resistant whitefly populations in addition, canaccelerate population growth.Cabbage Ecological Guide - 2000106

Major Cabbage Insect PestsRelated exercises from CABI Bioscience/FAO manual4-D.1 Predation on sucking insects in insect zoo4-D.2 Cage exclusion of natural enemies in the field4-D.7 Parasitism of whitefly5.11 Stemborer – Melanagromyza cleomaeDuring IPM training exercises in Lao PDR (1997) and northern and central Thailand (1999, 2000), thestemborer Melanagromyza cleomae was found in stems of cabbage seedlings and petioles of olderplants. Very little is known about this stemborer fly.M. cleomae appears to attack only crops in the crucifer family. It must be considered a potential pest onimportant crops on a wider scale than so far reported in literature (CABI ID report, 2000). Much of thedocumented information on M. cleomae in below section is based on innovative action-research byfarmers, IPM trainers and field-based researchers, during above mentioned IPM training exercises (pers.comm. J. W. Ketelaar, 1999/2000).Description and life cycleThe adult is a fly, approximately 2 mm long, mostly black with red eyes and a slight blue-green cast onthe back of the thorax and abdomen. Eggs are inserted into plant tissue. Larvae are small white maggotswith no legs. Pupation occurs inside the tunnels formed by the larvae in plant tissue.In northern Thailand, IPM trainers reared aromyzid stem borers and their parasitoids from weeds (compositefamily) surrounding the cabbage fields. These stemborers were identified as Melanagromyza metallica.This means that the cabbage stemborer is probably not using the prevalent composite weeds as alternativehosts. Further ecological studies are needed to study alternative hosts (pers.comm. Dr. M. Schmaedick,2000)Plant damage and plant compensationThe larvae (maggots) of this stemborer fly, bore into the main stems of cabbage plants, often youngcabbage transplants. The main symptom is plant stunting. The transplants usually survive but show veryweak growth, discoloration of leaves and do not form heads. In older plants the larvae are ofund boring inthe petioles of older leaves. It is not certain what effect, if any, this damage to the older petioles may haveon cabbage yield. Fields infested at this stage may, however, produce large numbers of flies that couldinfest nearby fields.Damage symptoms caused by the stemborer is often confused by farmerswith stunting due to lack of water or fertilizers.Serious crop damage occurred in young cabbage transplants during atraining activity in Chiangrai province, northern Thailand. Interestingly, itseemed that there was a difference in stemborer occurrence in the plotthat was fertilized according to Farmer Practice (high level of infestation)as compared to the IPM plot which received fertilizer according torecommended rate after soil analysis (low infestation). The main differencein fertilizer treatment was that the IPM plot received a high input of organicfertilizer, and the FP plot received only chemical fertilizers.larva in the stem or root107 Cabbage Ecological Guide - 2000

Major Cabbage Insect PestsThis could indicate that better fertilizer management (that includes organic material) made plants growquicker and therefore shorten the borer susceptible stage, or that IPM fertilizer treatment resulted inhealthier plants which were less susceptible to the stemborer. The higher organic matter in the IPM plotsmight have helped in population build ups of predators (including predatory fly Coenosa sp. (see below)).However, such hypothetical relations should be further studied. (Chiangrai TOT report, 1999)Natural enemiesTwo species of parasitoids, Eurytome sp. and Syntomopus sp. were reared from stemborer immaturestages from fields in Chiangrai, northern Thailand. Identification of these parasitoids was not yet doneupon printing of this guide.The predatory fly, Coenosa sp. may be a natural enemy for this stemborer. Coenosa is being used inGerman greenhouses for control of cabbage maggot (Delia sp.) Both the larvae in the soil and adultsabove ground are predatory. There is a strong link between population of Coenosa and earthworm andthus a likely link to organic matter content in the soil. Thus higher organic matter in the soil, such as infields where lots of compost is used, may help increase the population of predators (pers. comm. M.Schmaedick and J.W. Ketelaar, 1999/2000).However, such links should be further studied.Management and control practices· Selecting only healthy seedlings for transplanting.· Proper soil fertility management and using organic material, such as compost, may help increasecrop vigor and may help population build-up of predators.· Good sanitation, including weeding out and destruction of visibly damaged plants and remainingstubbles in the field, may help to prevent population build-up.¤Points to remember about stemborer:· The stemborer Melanagromyza cleomae can severely damage young transplants of cabbage,resulting in stunted plants and no head development.· Adding organic material possibly lowers infestation by stemborer but this needs to be confirmedwith more experiments.· Some parasitoids of stemborer were found, but identification and efficacy is not yet clear.Related exercises from CABI Bioscience/FAO manual:4-C.1 Sanitation to control shoot borersCabbage Ecological Guide - 2000108

Major Natural Enemies of Cabbage Insect Pests6MAJOR NATURAL ENEMIES OFCABBAGE INSECT PESTSSUMMARYPredators, parasitoids and pathogens are the main groups of natural enemies thatcan control large numbers of cabbage insect pests. This is why they are called“Friends of the farmer”.Predators: are usually generalists: not specific for one insect species or stage, infact they may even eat other predators or “neutrals” when there is not much foodavailable. Examples are ladybeetles, spiders, lacewings and hover flies. Predatorsare often the first “line of defense” when pest insect populations build up and theyfollow host insect population by laying more eggs when there are more hostinsects available. Predators are often effective natural enemies when pest populationsare high. Some species such as lady beetles and lacewings are (commercially)available for field release.Parasitoids: are usually specific for an insect. Parasitoids such as Diadegma sp.and Cotesia sp. are the most important natural enemies for diamondback mothcontrol and possibly for Pieris sp. Diadegma and Cotesia sp. are now (commercially)available in SE Asia for field releases.Pathogens: are usually host specific and require specific climatic conditions (usuallyhigh humidity) to be effective. Some pathogens, e.g. Bacillus thuringiensis (Bt)and NPV are (commercially) available for field releases and can give very goodcontrol. NPV and some fungal pathogens can be produced at farm level, afterbasic farmer training. Nematodes such as Steinernema sp. also increasingly availablefor insect control.Natural enemies:p Are easily killed by (broad-spectrum) pesticides.p (Indigenous) natural enemies can be attracted and conserved by not sprayingpesticides, allowing small numbers of insets in the crop, planting floweringplants or a trap crop at field borders, and prividing shelterr (e.g. straw bundles).109 Cabbage Ecological Guide - 2000

Major Natural Enemies of Cabbage Insect Pests6.1 PredatorsPredators are animals that kill and eat other animals. They can be verylarge animals like lions that kill and eat deers, cats that eat mice, orspiders that eat moths.Predators usually hunt or set traps to get their prey. They can kill orconsume many prey and are generally larger than their prey. They areoften generalists rather than specialists and can attack immature andadult prey. When there is not enough prey around they may even eateach other!Predators of insect pests can be divided into groups such as beetles, true bugs, lacewings, predatoryflies, predatory mites and others like spiders and praying mantids.Predators are especially important natural enemies because they can often survive when there are noinsect pests around. They can switch to other food sources like crop visitors or neutrals, insects that livein the field but do not attack cabbage plants. They may even eat each other in times of low foodavailability or move to the borders of the field to find prey. Predators are therefore often the first cropdefenders against pests. Predators follow the insect population by laying more eggs when there is moreprey available. When no predators are around, pests that arrive in the field can easily increase theirpopulation.In this section, a number of predators that are important for cabbage pest insect control are described.6.1.1 Lady Beetles - CoccinellidaeAlso called ladybugs, ladybird beetles or coccinellid beetles. There are manydifferent species of lady beetles. However, not all lady beetles are predators.Some, like Epilachna sp., are herbivores, particularly on solanaceous crops.Check feeding habits in insect zoo studies (section 4.4)!Primary prey: aphids, mites, whiteflies, small insects, insect eggs.Predatory stages: both adults and larvae.Description and life cycleAdult lady beetles are small, round to oval inshape. The typical species present in manyvegetables has black markings on red, orange oryellow forewings. Different species of ladybeetles have a different color or different markings.Both larvae and adults of lady beetles arepredators: they eat aphids, small caterpillars,mites and insect eggs. Many lady beetles prefera diet of aphids but may switch to other preywhen there are not enough aphids. The larvaehave a very different appearance from the adults.They are dark and look a bit like an alligator with3 pairs of legs. There are usually 4 larval instars.Lady beetles can consume many prey on a dayand can also travel around quite far (larvae maytravel up to 12 m) in search of prey.Life cycle of the lady beetle(from : Hoffmann et al, 1993)Cabbage Ecological Guide - 2000110

Major Natural Enemies of Cabbage Insect PestsFemale adults lay 200 to more than 1000 eggs in a few months time. The more food there is, the moreeggs it lays. That way, it can keep up with the pest insect populations. Eggs are usually deposited nearprey such as aphids, often in small clusters in protected sites on leaves and stems. The eggs are small(about 1 mm), cream, yellow or orange in color.The last larval instar pupates attached to a leaf or other surface. Pupae may be dark or yellow-orange incolor. Pupal stage takes about 3 to 12 days, depending on temperature and species. Adults live for a fewmonths up to a year and have several generations in a year.EffectivenessLady beetles are voracious feeders. As an adult, they may eat as many as 50 aphids per day. Each larvaeats 200 to 300 aphids as it grows. They are effective predators when the pest population is high: oneadult may eliminate all aphids from a seriously infested plant in just a few days. Lady beetles are thoughtto be less effective when pest densities are low. There may also be some crop damage before ladybeetles have an impact on an aphid population.Because of their ability to survive on other prey or on pollen when there are not so many aphids, ladybeetles are very valuable.In Thailand, at Biocontrol Centers of Dept. of Agricultural Extension, ladybeetles are reared and availableto farmers for field releases.ConservationLike many other natural enemies, lady beetles are easily killed by broad-spectrum insecticides. Avoidthe use of these pesticides as much as possible!Lady beetles benefit from shelter for protection from adverse weather conditions and for refuge whencrops are harvested. This shelter can simply be some plants around the field.6.1.2 Ground beetles - CarabidaePrimary prey: soil-dwelling beetles and fly eggs, larvae, pupae, other insect eggs, small larvae and softbodiedinsects, some caterpillars.Predatory stages: both adults and larvae are predators.Description and life cycleThere are many species of ground beetles. Adults ground beetles may bevery small (about 3 mm) to large (12 - 25 mm). Many are dark, shiny beetles,often with prominent eyes and threadlike antennae. Adult ground beetles arefound under stones and debris and they are active mainly at night. They canrun rapidly when disturbed or when in search of prey. Night-active species areblack. Those that are active during the day may be brightly colored or metallicin appearance.Eggs are usually laid singly on or in the soil near prey, sometimes in specially constructed cells of mudor twigs. The eggs can be soft, cylindrical with rounded ends and about 0.5 mm long. Some species layonly a few eggs, others may lay hundreds of eggs. Generally, the more food there is for a ground beetle,the more eggs it lays. That way, it can keep up with the pest insect populations.111 Cabbage Ecological Guide - 2000

Major Natural Enemies of Cabbage Insect PestsThe larvae usually have large heads with large jaws for holding and piercing prey. They look very differentfrom the adults. Most species pupate in the soil.You can catch ground beetles with pitfall traps in the field. See section 4.11.2.EffectivenessThe larvae and adults of several ground beetle species have been shown to eat many prey if given theopportunity. There is little field data on the efficacy of ground beetles. Their ability to cover large distancesin search of prey makes them a valuable addition to other natural enemies.ConservationGround beetles are easily killed by (broad-spectrum) insecticides. Avoid using these pesticides whenpossible.Shelterbelts can provide refuge for the adult beetles and can help them through a period of harvest andfield preparations for the next crop.6.1.3 Lacewings - ChrysopidaePrimary prey: aphids, spider mites (especially red mites), thrips, whitefly,eggs of leafhoppers, moths, and leafminers, small caterpillars, beetlelarvae.Predatory stages: larvae, adults of some species.There are several species of green lacewings (Chrysopa and Chrysoperla sp.). The common green lacewing,Chrysopa carnea is native to much of North America, several countries in Europe and in India. Apertochrysasp. was also found in India (Tamil Nadu). Another green species is Chrysopa rufilabris, which may bemore useful in areas where humidity tends to be high. Another species is the brown lacewing, which isbrown in color and about half the size of the green lacewing.Because in several areas in SE Asia, the common green lacewing C. carnea is the predominant species,this important predator is reviewed in this section.Description and life cycleAdult green lacewings are pale green, about 12-20 mmlong, with long antennae and bright, golden eyes. Theyhave large, transparent, pale green wings and a delicatebody. Adults are active fliers, particularly duringthe evening and night and have a characteristic, flutteringflight. Adults feed only on nectar, pollen, andaphid honeydew, but their larvae are active predators.Oval shaped eggs are laid singly at the end of longsilken stalks and are pale green, turning gray in severaldays. Several hundred small (less than 1 mm)eggs are laid, sometimes in clusters. The larvae, whichare very active, are gray or brownish and alligator-likewith well-developed legs and large pincers with whichLife cycle of the common green lacewing,Chrysoperla carnea(from: Hoffmann et al, 1993; www12)Cabbage Ecological Guide - 2000112

Major Natural Enemies of Cabbage Insect Peststhey suck the body fluids from prey. Larvae grow from less than 1 mm to about 6-8 mm, through 3 instarsin about 2 – 3 weeks.Mature third instars spin round, silken cocoons usually in hidden places on plants. Emergence of theadults occurs in 10 to 14 days. The life cycle is strongly influenced by temperature: the higher thetemperature, the quicker. There may be two to several generations per year.Lacewings can be found in a range of crops including cotton, sweet corn, potatoes, cole crops, tomatoes,peppers, eggplants, asparagus, leafy greens, apples, strawberries, and other crops infested byaphids.EffectivenessThese lacewing larvae are considered generalist beneficials but are best known as aphid predators.Laboratory studies from India show that lacewings preferred aphids to whiteflies. The larvae are sometimescalled aphid lions, and have been reported to eat between 100 and 600 aphids each, although theymay have difficulty finding prey in crops with hairy or sticky leaves.The appetite of lacewing larvae….In a trial from India it was found that during development, each larva of Chrysoperla carnea consumedan average of 419 aphids (Aphis gossypii), 329 pupae of whitefly (Bemisia tabaci) and 288 nymphsof jassid (Amrasca biguttula). In all cases, 3rd-instar larvae consumed the major portion of the totalnumber consumed (60-80%) (Balasubramani et al, 1994).There is potential for commercialization of Chrysopa sp. for use against a variety of pests and a lot ofresearch is ongoing on rearing methods and field effectiveness in SE Asia. In Thailand, at BiocontrolCenters of Dept. of Agricultural Extension, lacewings are reared and available to farmers for field release.In the USA and in some European countries like the Netherlands, C. carnea and C. rufilabris are availablecommercially, and are shipped as eggs, young larvae, pupae, and adults.C. carnea is recommended for dry areas, C. rufilabris for humid areas.Larvae are likely to remain near the release site if aphids or other prey are available. Newly emergingadults, however, will disperse in search of food, often over great distances, before laying eggs.J Predator of predators….!?! LNatural lacewing populations have been recorded as important aphid predators in potatoes, butmass releases of lacewings have yet to be evaluated against aphids in commercial potatoproduction. In small scale experiments outside the United States, lacewings achieved various levelsof control of aphids on pepper, potato, tomato, and eggplant, and have been used against Coloradopotato beetle on potato and eggplant. On corn, peas, cabbage,and apples, some degree of aphid control wasobtained but only with large numbers of lacewings. Massreleases of C. carnea in a Texas cotton field trial reducedbollworm infestation by 96%, although more recent studiesshow that C. carnea predation on other predators candisrupt cotton aphid control. That’s the negative side of ageneralist predator…. (ref. www17)113 Cabbage Ecological Guide - 2000

Major Natural Enemies of Cabbage Insect PestsConservationBecause young larvae are susceptible to drought, they may need a source of moisture. Adult lacewingsneed nectar or honeydew as food before egg laying and they also feed on pollen. Therefore, plantingsshould include flowering plants (e.g. at borders of the field), and a low level of aphids can be tolerated toattract and conserve lacewings.The green lacewing appears to have some natural tolerance to several chemical insecticides althoughthere may be considerable variation. Populations tolerant of pyrethroids, organophosphates, and carbarylhave been selected in the laboratory. Still, when lacewings (and other natural enemies) occur in the field,it is advisable to avoid using pesticides.6.1.4 Hover flies - SyrphidaeHover flies are also called syrphid flies or flower flies.Primary prey: aphids, small caterpillars, sometimes thrips, possibly jassid nymphs.Predatory stages: only larvae of hover flies are predators.Description and life cycleAdults of the hover fly eat pollen and nectar from flowers. Only the larvae are effective aphid predators.The adult hover flies look like bees or wasps and are usually seen near flowers. Many species havecompact, flattened bodies, large eyes and black and yellow stripes on the body. They vary in size from9 - 18 mm.The female lays single, small (about 1 mm), white eggs that lie flat on leaves or shoots near or amongaphid populations. Females can lay several hundred eggs. The larvae hatch in 2 - 3 days. The larvae aresmall maggots without legs, they look more like tiny slugs than adult hover flies. They vary in color fromcream to green to brown, depending on the species and the prey consumed. There are 3 larval instars.The larvae suck out the inside liquids of aphids and small caterpillars until only the skin remains!In about 2 weeks, the larva develops into a pupa which usually is pear-shaped and is cream, green orbrown in color. The pupa is attached to leaves or stems, sometimes in the soil.Predation efficacy hoverfly: a study exampleTo check how effective one hoverfly larva is, you can count how many prey it eats in a day. Collect afew hoverfly larvae from the field (use wetted hair brush to handle them). Put one larva per potted plantwith a known number of prey e.g. aphids on an cabbage leaf. Count how many prey is left after 24hours. Place the same number of aphids in a jar without the predator to check how quick the aphidpopulation grows when no predator is around. Use hoverfly larvae of different sizes (there are 3 larvalstages) and compare the appetites of each stage. Discuss if hoverflies can keep up with aphidpopulation growth.The period from egg to adult varies from 2 to 6 weeks, depending on the temperature, species andavailability of aphids. If there are many aphids for the hoverflies to eat, there can be more generations.Cabbage Ecological Guide - 2000114

Major Natural Enemies of Cabbage Insect PestsEffectivenessLarvae of the hover fly are voracious eaters. One larva may eat up to 400 aphids during its development!On a small scale, larvae can keep aphid populations in check but it is unknown if they manage to controlaphids in large fields.Life cycle and predation efficacy hoverfly: a study exampleWhen you know how many prey the different larval instars of the hoverfly larvae eat in a day, you cancalculate the efficacy during the whole larval stage. Collect the smallest sized hoverfly larvae thatyou can find (using a wetted hair brush to handle them). Rear them in separate pots (or they mighteat each other!) and feed them with fresh aphids every day. Handle the hoverfly larvae as little aspossible. Observe the changes in size, color and shape as the larva develops and note down theduration of each larval stage. Count how many days it takes for the hoverfly to develop into a pupa.Once it has become a pupa, it stops feeding.Calculate the total number of prey consumed of one larva with the results of the previous trial (numberof prey consumed per day per life stage x number of days the life stage takes).ConservationAs for almost all natural enemies, hover flies are easily killed by broad-spectrum insecticides. Avoid useof these pesticides when possible.Adult hover flies need flowering plants to feed on. They are attracted to weedy borders and gardenplantings. Flowers have an important function in attracting hoverfly adults. See also section 4.9 onconservation of NE’s.6.1.5 Spiders - AraneaePrimary prey: aphids, mites, moths, flies and beetles, depending on the speciesof spider. They may also attack other natural enemies.Predatory stages: nymphs and adultsDescription and life cycleSpiders are not insects but belong to the order of Araneae which have 8 rather than 6 legs. There aremany species of spiders and they can be roughly divided into two main groups: spiders that hunt insearch of prey and spiders that make webs and wait for prey to be caught in the web. Both types are verycommon predators in a vegetable field and they can be very voracious. Most hunting spiders are verymobile and spend a lot of time searching for prey. Web-makers are important predators of flying insectslike adults of moths.Like many other predators, the more prey spiders can consume, the more eggs will be laid by thefemale. This allows these predators to increase their numbers when the pest population increases.The number of eggs spiders can lay varies from a few to several hundreds, depending on the species.Some spiders carry the eggs in a little sac until the young spiders hatch from the eggs (e.g. wolf spiders– Lycosidae). Others guard the location where the eggs are deposited (e.g. lynx spiders) or place the eggmass in the web or on leaves, covered with fluffy silk. Spiders may live up to 4 months, depending on thespecies.115 Cabbage Ecological Guide - 2000

Major Natural Enemies of Cabbage Insect PestsEffectivenessSpiders are voracious predators: it depends on the species how many prey it caneat on a day. Some spiders can eat as many as 5 large insects per day!ConservationMulching, especially organic mulch, can increase the number of spiders in vegetable crops becausespiders can hide in the layer of mulch and they find protection from sun and rain.Spiders are easily killed by broad-spectrum insecticides. Avoid using pesticides as much as possible.6.1.6 Praying mantids - MantidaeAlso called praying mantis.Primary prey: flies, bees, moths and small spiders.Predatory stages: nymphs and adults are predators.Description and life cycleBoth adult and nymphs have large frontlegs that they hold in a “praying”position. The nymphs look like smalladults.The adults are good flyers and cantravel long distances. Adults are lightgreen to brown in color and can be 5 -10 cm long. The eggs are placed in apapery mass (“egg case”) attached toa twig.an adult praying mantidmantid egg massEffectivenessMantids are very active predators of many insects and they serve a beneficial role in destroying manypest insects. They are indiscriminate hunters and can eat many large insects per day.However, mantids are usually not considered to be important in regulating insect pest populations.ConservationAs for almost all natural enemies, praying mantids are easily killed by broad-spectrum insecticides.Avoid use of these pesticides when possible.When the egg cases of praying mantids are seen attached to trees or places outside the field, they maybe carefully removed and placed in the cabbage field. The young nymphs may start feeding on pestinsects of cabbage.Cabbage Ecological Guide - 2000116

Major Natural Enemies of Cabbage Insect Pests6.2 ParasitoidsThere is often confusion between the terms parasitoid and parasite.Insect parasitoids are organisms that have an immature life stagethat develops on or inside a single insect host, consuming all or mostof its tissues and eventually killing the host. This is why parasitoidsare important as natural enemies of insect pests. Adult parasitoidsare free-living.pupal parasitoidA parasite also lives in or on another organisms (the host) during some portion of its life cycle, but thisdoes not always lead to the death of the host.Most beneficial insect parasitoids are wasps but there are also flies and other insects that are parasitoids.Parasitoids are usually smaller than their host and they are specialized in the choice of their host. Theyusually attack only one stage of the host insect: eggs, larvae or pupae. Parasitoids are often called aftertheir stage preference, for example “egg parasitoids” attack only eggs of a particular insect. Only femalessearch for hosts, they usually lay eggs in or near the host.SEX: male or female...?In wasps, the sex of a parasitoid off-spring is determined differently than for other animals. In parasiticwasps, females come from fertilized eggs and males come from unfertilized eggs. So if a femaledoes not mate with a male wasp, she will produce only males. If she does mate, she will produce amix of both males and females, usually more females. And that is important because only femalesare able to parasitize other insects! Males are only useful for mating...!Whereas insect predators immediately kill or disable their prey, pests attacked by parasitoids die moreslowly. Some hosts are paralyzed, while others may continue to feed or even lay eggs before they diefrom the parasitoid attack. Parasitoids, however, often complete their life cycle much more quickly andincrease their numbers much faster than many predators.Parasitoids are following the pest population, unlike predators, they cannot increase their own populationwithout their host insects. It is therefore always good to have at least a few pest insects in the field. Theyserve as food and as a host for the natural enemies!Parasitoids can be the dominant and most effective natural enemies of some pest insects, but becausethey are so small, their presence may not be obvious. This is why it is so important to monitor fields orthe friends of the farmer will never be noticed, in fact, will perhaps be treated with pesticides instead ofgratitude! L?A parasitoid parasitized??Yes, unfortunately, it is possible: also a parasitoid of insect pests can be parasitized by otherparasitoids: this is called hyperparasitism. Hyperparasitoids are even smaller than parasitoids.Hyperparasitism can be common, and may reduce the effectiveness of some beneficial species,especially in case of introduced natural enemies (those natural enemies that are brought into a fieldfrom outside) . Little can be done to manage hyperparasitism.LThe life cycle and reproductive habits of beneficial parasitoids can be complex. In some species, (e.g.Diadegma) only one parasitoid will develop in or on each pest while, in others (e.g. Cotesia glomerata),hundreds of young larvae may develop within a single host.117 Cabbage Ecological Guide - 2000

Major Natural Enemies of Cabbage Insect PestsRecognizing parasitoid activitiesParasitoids are difficult to spot because they are very small and they are fast flyers. However, theyleave evidence of their activities. In the case of diamondback moth (DBM) parasitoids for example,dead caterpillars or, more commonly, cocoons can be found. Often, these cocoons are wronglythought to be eggs of insect pests. A good way to study parasitoids is to collect sick insects,cocoons, round or egg-shaped masses of spiders and even insects caught in spiders webs in thefield. These can be observed in jars or clear plastic bottles. If cocoons are found next to a dead ordying caterpillar, the connection between cocoon and caterpillar can be shown. For example, a whitecocoon of Cotesia plutellae is usually found next to a dead caterpillar with a large hole indicatingwhere the parasitoid larva emerged. After emergence, the larva spins a cocoon.Many insect pest larvae of similar age could be collected to confirm ifthe parasitoid is coming out of the caterpillar, and witness the processof emerging. Showing this will help farmers understand the importanceof the cocoons.Placing cocoons inside clear plastic bottles helps to observe what emerges from the cocoon. Drawthe cocoons, the dead caterpillar and the type of adults that emerge, using color pencils (Ooi, 1999).See also box below.Most parasitoids only attack a particular life stage of one or several related species. The immatureparasitoid develops on or within a pest, feeds on body fluids and organs, and either comes out of the hostto pupate or emerges from the host as an adult. The life cycle of the pest and parasitoid can coincide, orthat of the pest may be altered by the parasitoid to accommodate its development. Parasitoids areusually grouped into several broad categories based on their development patterns. Egg parasitoidsattack the egg stage of their host, larval parasitoids attack the larvae etc.To determine if there is any parasitism and to what extent, it is often necessary to rear samples of pestinsects to see if any adult parasitoids emerge (see box below).Some parasitoids take longer to develop than their host. To study these parasitoids, it is important to beable to rear the collected egg masses or immature stages of the insects. If collected material is kept insuitable containers or cages, be sure to keep specimen for at least one month and even after it looks likeeverything has already emerged.Rearing Parasitoids: A Study ExampleAn easy method to rear parasitoids, for example of cabbage aphids, is the following:· Collect a number of cabbage leaves with large colonies of aphids on the underside.· Check, if possible with hand lens, if there are any “mummies” (swollen, dead aphids that havebeen tanned (often brownish) and hardened).· When mummies are found, place the leaf with aphids in a jar (insect zoo), together with a pieceof tissue to avoid condensation. Close the jar with a fine netting.· Monitor changes in aphids and mummies over the next few days.· Other aphids that have been parasitized, will transform into mummies in the next few days.Adult parasitoids (possibly Diaeretiella rapae, see section 6.2.1) will emerge from the mummy.After emergence, you can see the exit hole towards the end of the aphid’s abdomen.Leaves containing aphid mummies can be redistributed to help spread the parasitoids.Cabbage Ecological Guide - 2000118

Major Natural Enemies of Cabbage Insect PestsRelated exercises from CABI Bioscience/FAO manual1.6 Show effects of beneficials incl. natural enemies6.2.1 Diaeretiella rapaePrimary host: aphidsDescription and life cycleDiaeretiella rapae is a small waspthat attacks only aphids. The adultwasps are very small, less than 3mm, and dark with long antennae.Adult wasps are usually active onbright, clear days. They may notfly on very hot, windy or rainy days.female lays egg in aphidlarva develops in aphidpupa in swollen aphid mummyFemales lay up to several hundredeggs. They prefer to lay eggs inadult emergesaphid nymphs rather than adults.One wasp larva develops within one(from Hoffmann et al, 1993)aphid. Parasitized aphids look like “mummies”: swollen, dead aphids that are brownish in color and havea hardened, papery skin to form a protective case for the developing wasp pupa inside. The mummiesmay occur within an aphid colony or be found singly on leaves or stems.The larva inside the aphid either spins a cocoon under the dead aphid or pupates within the mummifiedaphid. The adult wasp emerges after cutting a circular hole in its cocoon.Adults live from 1 to 3 weeks and there can be many generations per year. They can occur in manyvegetable crops with aphid populations.EffectivenessDiaeretiella rapae can have an effective impact on aphid infestations. Females of some species mayparasitize hundreds of aphids in one day. If young aphids are parasitized, they will usually die beforereproducing. Aphids parasitized as older nymphs or as adults may reproduce before dying but producefewer young aphids than normal. The effectiveness of this wasp in cooler areas is not clear.Mummy monitoringMonitoring just the number of aphid mummies will not give the right estimation of the degree ofparasitism by wasps. It does not account for the parasitized aphids that have not yet becomemummies. Also, parasitized aphids may move away from the feeding site or fall off the plant.It does tell you if the parasitoid Diaeretiella is present and active and it gives anidea of the amount of parasitism.In cases where aphids transmit virus diseases (that cause injury to plants),aphid parasitoids will generally not provide adequate control. Since the virus is transmitted within afew seconds after the aphid starts sucking the plant, this happens in a few seconds and whether ornot that aphid is parasitized does not matter for the spread of virus.119 Cabbage Ecological Guide - 2000

Major Natural Enemies of Cabbage Insect PestsConservationLeaves containing aphid mummies can be redistributed to help spread the parasitoids in the field. Checkif the parasitoids are still inside the mummies: when you see a circular hole in the mummy or in thecocoon of the parasitoid, the adult has emerged and it is useless to redistribute that leaf.Most parasitoids are even more susceptible to pesticides than predators. Adult parasitoids are usuallyalso more susceptible to pesticides than their hosts. Immature parasitoids may sometimes be protectedwhen they are inside the host or in their egg or cocoon, but when the host is killed, the immatureparasitoid will also be killed.Many adult wasps feed on insect honeydew, and nectar from flowers. When there is a lot of this foodavailable for the adult wasps, they live longer and lay more eggs, resulting in a higher percentage ofparasitism. Adult wasps are attracted to flowering plants near the field, such as mustard plants that canalso be used as a trap crop (see section 3.10). They also benefit from a source of water nearby.6.2.2 Diadegma speciesPrimary prey: larvae of diamondback moth.Diadegma sp. belong to the family of Ichneumonid wasps. This family has many members that arenatural enemies of vegetable insect pests. Some species of the genus Diadegma that are parasitoids ofdiamondback moth (DBM) are:· Diadegma semiclausum (Hellen) (Hymenoptera: Ichneumonidae)· Diadegma insulare (Hymenoptera: Ichneumonidae)· Diadegma eucerophaga (Hymenoptera: Ichneumonidae)D. semiclausum is very efficient in keeping DBM populations low at temperateconditions. It is mass-produced and released in highland cabbage growing areasin many countries, such as Philippines (see box below), Malaysia, Indonesia, andVietnam. However, it does not perform well at temperatures above 25C. As aresult, DBM is still a problem in tropical lowland areas. D. insulare may havepotential for DBM control in tropical lowland areas. Introduction of D. insulare isbeing considered, e.g. in Vietnam and Philippines.Diadegma adultDescription and life cycleDiadegma semiclausum is a small black wasp of about 5 - 7 mm long. Diadegma insulare looks verymuch like Diadegma semiclausum: it also is a small black wasp but it has reddish-brown legs and body.Females of both Diadegma semiclausum and Diadegma insulare insert one egg into the host larva. Alllarval stages are accepted for parasitism except the first stage due to its mining activity. The parasitoidhas a slight preference for the second and third instar.Female wasps search holes in damaged cabbage leaves with their antennae, indicating where DBM maybe present.Larvae that are parasitized do not look and behave differently from the unparasitized larvae since theparasitoid larva synchronizes its development with the development of the DBM larva. Only when thehost larva has completed its cocoon, the parasitoid larva inside will eat the host. It spins its own cocooninside the webbing of the DBM cocoon. The cocoon can be recognized because it is a double cocoonwhich may have a pale-white waist band. Diamondback moth cocoons are white inside (green when thelarvae first form the cocoon); Diadegma wasps are visible as dark bodies inside the cocoon, before theadult Diadegma emerges.Cabbage Ecological Guide - 2000120

Major Natural Enemies of Cabbage Insect PestsThe life cycle from egg to adult Diadegma semiclausum takes about 3 weeks. Females start laying eggsone day after emerging from the cocoon. During the first 2 or 3 days, they lay only unfertilized eggs thatresult in male wasps.EffectivenessDiadegma semiclausum is well adapted to temperate conditions: a temperature of 23 o C is considered tobe the optimum whereas at temperatures above 30 o C, the parasitoid will loose its effectiveness. Undertemperate conditions, the female adults of Diadegma semiclausum have a lifespan of about 3 weeks andwill parasitize 35 to 50 DBM larvae daily. That means every female can kill up to 1000 DBM larva in its life!In Philippines for example, 75% DBM parasitation was obtained by field releases of D. semiclausum infarmers’ fields (Ref. V. Justo, workshop biocontrol agents).Unfortunately, when the temperature rises, the lifespan and parasitism capacity decline rapidly. Thismeans Diadegma semiclausum is not suitable for effective DBM control at lower altitudes.Diadegma insulare may be more effective at lower altitudes. Diadegma insulare is the most importantparasitoid of the diamondback moth in North America and Canada. Native populations of D. insulare haveparasitized up to 70% of diamondback larvae in field trials in New York and from 50% to almost 90% inWisconsin (Grafius, www15).Studies in Asia to rear and test Diadegma insulare are ongoing, for example in Philippines.Field releases of Diadegma semiclausum in the Philippines: how is it done?Diadegma semiclausum can be released in the field as cocoons or as adult wasps.Distributing cocoons is easy because they are stronger than adultwasps and can survive longer transportation between the rearing stationand the field. In the field however, the pupae need protection frompredators like ants. They should protected until emergence. Usually,releasing adult wasps is recommended. Even though for the transport aspecial cage is necessary, loss from predation in the field is avoided and inaddition, the number of males and females can be decided before release (only females are parasitoidsof DBM!)As a general rule, about 200 - 300 females and 100 - 150 males are distributed over a 1 hectare area.If the wasps can be established on the release site, it will act as point of dispersal for neighboringfields. Usually, adults are released at the same site several times (4 - 6) at weekly intervals. Thisincreases the chance of taking action at the right time for release, and speeds up the build-up of thefield population by closing the gaps between generations.(Koenig et al, 1993)ConservationDiadegma sp. can give very effective control of DBM if their populations are conserved through limitinguse of chemical insecticides. This requires the cooperation of many farmers in an area. The first step inconserving Diadegma wasps (and other natural enemies) is to monitor fields, and observe and count thepresence of pests and the degree of parasitism.For those farmers who still want to use pesticides (despite the fact that DBM has become resistant tomany chemical pesticides, and even to Bt – see box in section 5.1), they could be encouraged to use Btpreparations or to spot spray: only on the heart and later the head of specific plants, not on the whole121 Cabbage Ecological Guide - 2000

Major Natural Enemies of Cabbage Insect Pestsfield. The head of cabbage is the marketable part and needs protection against feeding of pests. Theouter leaves will be removed anyway and can serve as a reservoir for DBM to be parasitized by Diadegmawasps.It should be noted that application of Bt kills DBM larvae, including the parasitized DBM larvae. Thatmeans the parasitoid larva inside the DBM is also killed! Adult parasitoids, however, survive a Bt application.For the longer term establishment of Diadegma wasps, the area should provide enough cabbage fields(not only in terms of size but also in year-round cabbage production) to support survival of the parasitoid.Diadegma females require nectar sources to feed on. A nectar source can increase D. insulare femalelongevity from 2-5 days to more than 20 days (Grafius, www15). And the longer it lives, the more eggs itcan lay.Allowing wildflowers (especially cruciferous weeds) to grow around the fields, and allowing DBM tocolonize those weeds, will increase the abundance and effectiveness of Diadegma wasps for managementof DBM.FARMER TRAINING is essential for successful parasitoid introduction!When farmers…· recognize that DBM is not effectively controlled by chemical pesticides,· understand how parasitoids work,· understand that parasitoids are killed by chemical pesticides,· recognize parasitoid activity in the field, and know how to quantify it, ....................…they’llappreciate the work of parasitoids in the control of insect pests !6.2.3 Cotesia speciesPreviously called: Apanteles sp.Cotesia species belong to the family of Braconid wasps. The genus Cotesia hasmany members that are natural enemies of vegetable insect pests. Some of thebeneficial Cotesia relevant to cabbage are:· Cotesia glomerata: parasitoid of the cabbage white butterfly, Pierisrapae and Pieris brassicae.· Cotesia plutellae: parasitoid of diamondback moth, Plutella xylostella.· Cotesia marginiventrus: parasitoid of the cabbage looper, Trichoplusia ni.· Cotesia rubecula: parasitoid of the cabbage white butterfly Pieris rapaeCharacteristics of Cotesia glomerata and Cotesia plutellae are described below.Cotesia glomerataadultDescription and life cycleAdults of Cotesia glomerata are small, dark colored wasps of about 7mm length. Their antennae are long and curved. First and secondinstar larvae of Pieris sp. are attacked and serve as the host for theyoung wasps. The female wasp lays 20 to 60 eggs inside the hostcaterpillar. This caterpillar may still live for some time while the larvaedevelop inside but eventually it dies. The parasitoid larvae will emergeA large cabbage whitebutterfly larva with cocoonsof cottesia glomerata(from: Kirk, 1992)Cabbage Ecological Guide - 2000122

Major Natural Enemies of Cabbage Insect Pestsfrom the caterpillar after some time to spin their silken cocoons on or very nearto the host caterpillar. The cocoons are usually found in an irregular mass nextto the dead caterpillar.Adults of Cotesia plutellae are also small black wasps. Females live only ashort time: about 10 days, depending on environmental conditions. Total lifecycle from egg to adult takes about 25 days.Cotesiaplutellae adultCotesia plutellae lays its egg inside a DBM larva. The parasitoid larva developsinside the DBM caterpillar. When fully grown, the parasitoid larva emergesfrom the side of the DBM body and it spins a silken cocoon for pupation. Thecocoons are white and can usually be found attached to the under surface ofthe leaves.larvae develop in caterpillarfemale lays egg in caterpillarpupae in silken cocoonsadults emerge(from Hoffmann et al, 1993)EffectivenessCotesia glomerata is reported to be a very effective control agent of cabbage butterflies Pieris sp. In theU.S.A., more than 80% of the caterpillars may be parasitized in fields unsprayed by chemical insecticides(ref. www16).Cotesia plutellae can give effective control of diamondback moth. In studies (1995) in the highland area ofDalat, Vietnam, Cotesia was found soon after DBM occurred, and reached parasitism levels up to 90%.In the lowlands of Hanoi area (1994-1995), parasitism was not more than 22% on average. (FAO -Updates on Vietnam national IPM programme in vegetables, 1999)Studies show that Cotesia plutellae can reach high parasitation levels when pest populations are alreadyhigh, but is less effective at lower pest densities (FAO Dalat report (V.Justo), 1998).Cotesia can be naturally present in fields. Several Cotesia parasitoids are commercially available, forexample in the U.S.A. Mass-rearing houses have also been established in Philippines (FAO Dalat report(V.Justo), 1998) and will be established in Vietnam. In Lao PDR, Cotesia is being reared and releasedwith assistance of the AVRDC.In addition, C. glomerata may be a vector in the transmission of a granulosis virus in cabbageworm,Pieris rapae (ref. www16).123 Cabbage Ecological Guide - 2000

Major Natural Enemies of Cabbage Insect PestsConservationLike almost all other predators and parasitoids, Cotesia sp. are quickly eliminated when spraying chemicalinsecticides. When Cotesia is active in the field, avoid using insecticides when possible. Insecticideapplication may actually lead to an increase of pest insect populations because the natural enemies arekilled (see section 4.11.11 and box in section 5.1).6.2.4 Diadromus collarisHost: pupae of diamondback moth (DBM).The wasp Diadromus collaris belongs to the family of Ichneumonidae.Adult females are about 6 mm long with an obvious ovipositor.This DBM parasitoid was originally from Europe and came to Asia via Australia. It was introduced toVietnam in 1997. It is reared and has been released in the field in Dalat, a highland area in Vietnam. Therelease in Dalat is being carried out in conduction with monitoring and ecological studies by Farmer FieldSchools and farmer study groups (FAO progress report ’96 – ‘99). Initial results, however, show a lowparasitism percentage.In other studies, parasitism of pupae of 1 to 12% has been recorded (Hoffmann, 1993).Diadromus collaris complements the action of the larval parasitoid, Diadegma semiclausum. Togetherwith D. semiclausum, Diadromus collaris helps keep diamondback moth populations low, especiallywhen there is low (or no) use of chemical insecticides.6.3 PathogensPathogens are bacteria, viruses, fungi, and nematodes. Insects, like humansand plants, can be infected with pathogens which cause diseases. Insectpathogens generally kill, reduce reproduction, slow the growth or shorten thelife of a pest insect. Under certain conditions, such as high humidity or highpest populations, these pathogens can cause disease outbreaks that reducean insect population. This is why such pathogens can be considered naturalenemies of insects. Most insect pathogens are specific to certain groups ofinsects and certain life stages of the insect. Some microbial insecticides mustbe eaten by the target pest to be effective, others work when in contact with thetarget pest.Unlike chemical insecticides, microbial insecticides usually take longer to kill or weaken the target pest.J Most insect pathogens are not harmful for other beneficial insects, Jand none are toxic to humans.Pathogens are most effective when pest populations are very high. Pathogens are difficult to managebecause their presence and effectiveness strongly depends on factors like temperature and humidity.During the dry season for example, you will almost never see aphids killed by a fungus because thatfungus needs a high humidity for survival and spread.Cabbage Ecological Guide - 2000124

Major Natural Enemies of Cabbage Insect PestsMost pathogens are too small to be seen by human eyes. Only the symptoms that insect-pathogenscause can be seen with the eyes: for example a dead insect covered with fungus spores like “hairs” or“dust” or a dead insect which is black and spills fluid out of the body.Some pathogens have been mass produced and are available commercially for use in standard sprayequipment. These products are often called biocontrol agents, microbial insecticides, microbials, bioinsecticidesor biopesticides. Some of these microbial insecticides are still experimental, others havebeen available for many years. The best known microbial insecticide is probably the bacterium Bacillusthuringiensis or Bt which is available in many different formulations. NPV is increasingly being used inAsia because it can be produced on-farm. See section 6.3.3 below.Microbial insecticides can be used together with predators and parasitoids. Beneficial insects are notusually affected directly by the use of a microbial insecticide, but some parasitoids may be affectedindirectly if parasitized hosts are killed.Below, some pathogens of cabbage insect pests are described.6.3.1 Bacillus thuringiensis (Bt).Bacillus thuringiensis (Bt) occurs naturally in the soil and on plants. However, in the field, Bt is usuallyapplied as a microbial insecticide. There are different varieties of Bt. Each Bt variety produces a proteinthat is toxic to specific groups of insects.Some of the varieties of Bt with some of their target insect groups are:Bt var. aizawai Caterpillars, including diamondback mothBt var. kurstaki CaterpillarsBt var. tenebrionis: Colorado potato beetle, elm leaf beetleBt var. israelensis Mosquito, black fly and fungus gnat larvaeBt has been available as a commercial microbial insecticide since the 1960s and is sold under varioustrade names. Since 1985, the importation of Bt in Asia has greatly increased and Bt products are nowlocally produced, for example, in Vietnam and Thailand. Bt products are generally effective and safe fornatural enemies and non-target insects and can be used until close to the day of harvest. Bt can beapplied using conventional spray equipment. Good spray coverage is essential because the bacteriamust be eaten by the insect to be effective.Formulations of Bt var. kurstaki are available for the control of many caterpillar pests of vegetables.Some of the Bt brand names are: Dipel, Javelin, Biobit, MVP, Xentari, Agree. There may be many morebrand names and they vary per country.Mode of action and symptomsThe toxin inside the bacterium is only effective when eaten in sufficient quantity by the target insect. TheBt is sprayed over the leaves and when the insect eats the leaves, it will also eat the Bt. The toxindamages and paralyzes the gut of the insect. The toxin can only affect insects that have a specific gutstructure, that’s why Bt is specific for certain insect groups.Affected larvae become inactive, stop feeding and die from the combination of starvation and damage ofthe gut by the toxins of the bacterium. The larva may have a watery excrement and the head capsulemay appear to be overly large for the body size. The larva becomes soft and dies usually within days ora week. The body turns brownish-black as it decomposes.125 Cabbage Ecological Guide - 2000

Major Natural Enemies of Cabbage Insect PestsEffectivenessTo obtain effective control of the caterpillars, it is essential to apply Bt at the correct target species, at thesusceptible stage of development, in the right concentration, at the correct temperature and beforeinsects bore into the plants where they are protected. Young larvae are usually most susceptible.Caterpillars have to eat sufficient quantities of Bt in order to be affected and die. When they eat just alittle Bt, they may not die but their growth is retarded.ÕSunshine and Bt, not a good match...!?The Philippines highland vegetable FFS programme included a specific experiment for farmers toobserve the effect of sunlight on the efficacy of Bt products. They compared feeding and death rateswhen DBM larvae were placed on cabbage leaves which had been sprayed with Bt at different timesof day and hence received different sunlight exposures. The results showed that sunlight deactivatesBt. By discussing the results, the farmers were able to decide the best time of day to applybiopesticides, avoiding application when the sun is strongest (CABI, 1996).Bt only works at temperatures above 15 o C. Bt formulations are deactivated by sunlight. This is a reasonthat Bt is only effective for one to three days. Rain or overhead irrigation can also reduce effectiveness bywashing Bt from the leaves.Using Bt = patience?!?L It was noted that some farmers concluded after spraying Bt that “it didn’t work” because thecaterpillars were still alive. Some farmers even sprayed a chemical insecticide only one day afterapplying Bt.J However, only when looking more closely, they found that the caterpillars were actually hardlyeating anymore, they were just sitting on leaves, not moving very much. This is most important:when they stop eating, they stop damaging the crop! Bt is a stomach poison and the toxin paralysesthe stomach. Death by starving takes some time and, caterpillars will be dead after three days. Alsosee box below about testing Bt.(pers. comm. Dr. P.Ooi, 1999)ConservationBt formulations are applied like an insecticide. The Bt formulations become inactive after one to threedays. That means the bacterium inside the formulation is dead. Bt spores do not usually spread to otherinsects or cause disease outbreaks on their own. Therefore, conservation methods, as is important forpredators and parasitoids, are not relevant for Bt.Cabbage Ecological Guide - 2000126

Major Natural Enemies of Cabbage Insect PestsTesting Bt : a case from Dalat, VietnamTesting Bt is not like testing chemical insecticides. In pesticide studies, usually the number orpercentage of dead caterpillars is counted. Bt works differently from pesticides. It is important to helpfarmers recognize that Bt is working if there is less damage on the leaf, less frass production, andless caterpillar activity. Therefore, a different scoring system is needed to analyze data from Bt trials.Caterpillars affected by Bt do not die immediately. They usually stop feeding after 6 hours. Thisresults in less damage to the leaf and less frass production. At 24 hours after exposure to Bt, larvaeare dying: they do not move much and are lethargic. Larvae die after about 3 days.For Bt trials studying the effects of different types of Bt on DBM, the following scoring system toevaluate larval activities after Bt sprays was found to be very useful by farmers in Dalat, Vietnam:A. Leaf damage 1 = low 2 = moderate 3 = highB. Frass production 1 = none 2 = little 3 = muchC. State of DBM larvae 1 = dead 2 = dying 3 = activeFarmers in Dalat were very excited about this scoring system because it provided a better opportunityto study how Bt works. They observed that just counting dead caterpillars in Bt studies is not enoughand may even lead to a false conclusion.(Ooi, 1999)6.3.2 FungiThere are fungus species that can infect and kill insects. These fungi arecalled insect-pathogenic fungi or entomopathogenic fungi. These fungi arevery specific to insects, often to particular insect species, and do not infectanimals or plants. Most insect-pathogenic fungi need humid conditions forinfection and development but some fungus species can also infect insectswhen it is dry.There are also fungus species that infect and reduce fungi that cause plant diseases. These are calledantagonists. An examples of an effective antagonist is Trichoderma (Gliocladium). This section describesinsect-pathogenic fungi only. Antagonists are described in section 7.10.There are several fungus species naturally present in ecosystems and these may control some insectspecies when conditions like humidity and temperature are favorable. Such fungi can spread quickly andsome may also control sucking insects like aphids and whiteflies that are not susceptible to bacteria(e.g. Bt) and viruses. Management practices may be focussed on preserving and possibly augmentingthese natural enemies. Some fungi are commercially available in some countries in formulations that canbe applied using conventional spray equipment. Some experiences from Asia are listed below.Some common insect-pathogenic fungi:· Beauveria bassiana: this fungus is found naturally on some plants and in the soil. It needs warm,humid weather for spread and infection. Infected insect larvae eventually turn white or gray. Thisfungus has a broad host range: it can infect larvae of rice insects like black bugs and rice seed bugsbut also pests of other crops like corn borer, Colorado potato beetle and Mexican bean beetle. It isbeing tested for use against many other pest insects. Unfortunately, some natural enemies such aslady beetles can be susceptible to Beauveria. One possible application method that may avoidharming beneficial insects is the use of fungus-contaminated insect baits that are only attractive topest species.127 Cabbage Ecological Guide - 2000

Major Natural Enemies of Cabbage Insect PestsIn Indonesia (West Sumatra), Beauveria is used as a spraying solution for control of different pestinsects in chili (FAO Dalat report, 1998).· Entomophthora sp.: this fungus is fairly specific with regard to the groups of insects affected.Susceptible insects include aphids and several species of flies (in case of Entomophthora muscae).In Indonesia, an Entomophthorales (and the fungus Nomuraea rileyi) has been found on the cabbageheart caterpillar Crocidolomia binotalis. However, methods for production and distribution for thesefungi have not been developed (FAO Dalat report, 1998).· Metarhizium species: is being tested as natural enemy of corn rootworm, white grubs, some rootweevils and several other pest insects. It has a very broad host range and most species occur widelyin nature. Metarhizium anisopliae (also known as Entomophthora anisopliae) can be used to controla range of coleoptera and lepidoptera pests. Metarhizium can be an important control agent ofaphids. In Indonesia (West Sumatra), Metarhizium is used as a spraying solution for control ofdifferent pest insects in chili. In Philippines, Metarhizium effectively reduced populations of rhinocerosbeetles in coconut (FAO Dalat report, 1998). Metarhizium is commercially available as a foliar spray.See “The Biopesticide manual” (BCPC, 1998) for product names and manufacturers or check internetsites such as www25 and www29 (chapter 12, Reference list).· Nomuraea rileyi has been found in Indonesia as a control agent for the cabbage heart caterpillarCrocidolomia binotalis (FAO Dalat report, 1998). Methods for production and distribution of thisfungus have not been developed. More study is needed to evaluate the effectiveness of this fungusbut there may be potential for development, especially because at present there are no other goodbiocontrol options for the cabbage heart caterpillar.· A species of Paecilomyces was found infecting whiteflies on cabbage in Cebu, Philippines.Researchers from the Regional Crop Protection Center have isolated the species and are now massproducingit on artificial media (FAO Dalat report, 1998). In other countries, for example USA,Paecilomyces fumosoroseus is commercially available for whitefly control. It can be applied as aspore solution and it has some activity against aphids, thrips and spider mites.· Zoophthora radicans has a wide host range. It has been found infecting cabbage aphid (Brevicorynebrassicae), and larvae, pupa and adults of diamondback moth (Plutella xylostella). This fungus formsa white to tan colored mat of hypae (fungus threads) that covers the insect completely. Numerousspores are formed on this mat. Because Z. radicans is found is such a wide host range, it issuspected that this may actually be a complex of species, each with a more restricted host range(Shepard et al, 1999).· Verticillium sp. is used in Europe against greenhouse whitefly, thrips and aphids, especially ingreenhouse crops where controlled environment favors fungus effectiveness. Verticillium lecani iscommercially available in Europe and USA for the control of greenhouse whitefly.It is not important to know all the Latin names of insect-pathogenic fungi!What is important is that you can recognize them in the field and realizethat they are killing insects and this is to the benefit of the farmer!Cabbage Ecological Guide - 2000128

Major Natural Enemies of Cabbage Insect PestsPrimary Œ or secondary ???When you leave a plate of food with for example some chicken meat in your kitchen and leave it fora few days, you may find the meat covered with fungus when you look again. This fungus is called asecondary infection: it was not the reason the chicken died (the chicken was probably killed formeat) but it came in after the chicken was dead.Similarly, when insects are dead, some fungi may start growing on the dead insect. This is alsocalled a secondary infection. These fungi that cause secondary infection are part of the “trashmenteam” of nature: they make sure dead things are decomposed quickly. When the fungi actuallycause a living insect to die, like insect-pathogenic fungi do, it is called a primary infection.Interesting, but why bother?When searching for beneficials in the field, it is important to distinguish between pathogens causingprimary infection and those causing a secondary infection. Insects with a secondary infection mayoften be already partly decomposed.Knowing that there is a fungus controlling pest insects in your field, should make you extra carefulwhen considering pesticide applications, especially fungicides. Fungicides can quickly kill the beneficialfungi!How to use this…?When a primary infection is suspected and there are many insects dead and covered with fungus,you can consider making your own bio-insecticide from these dead insects. Collect as many as youcan find in the field, put them in a jar with water, crush them a little and stir firmly. This will releasefungus spores into the water. Filter the water slightly to remove large insect parts. The remainingsolution can be used to test its effectiveness in insect zoos. Spray the solution over insects that areplaced in a jar. Check if these insects become infected over the next days. Use water as a control.See also box in section 4.9. If it works, similar solutions can be applied to the field. It might giveadditional control of pest insects.J Free help from Mother Nature!Mode of action and symptomsFungi penetrate the skin of insects. Once inside the insect, the fungus rapidly multiplies throughout thebody. Death is caused by injury to the tissue or, occasionally, by toxins produced by the fungus. Thefungus emerges from the insect’s body to produce spores that can sometimes be seen as a “dusty”appearance. When spread by wind, rain or contact with other insects, the spores can spread the infection.Infected insects stop feeding and become lethargic. They may rapidly die, sometimes in a position stillattached to a leaf or stem. The dead insect’s body may be firm or it may be an empty shell. The fungusis often seen as “hairs” or “dust” in various colors around the insect’s body or on parts of the body.EffectivenessInsect-pathogenic fungi usually need moisture to cause infection. Natural infectionsare therefore most common during the wet season. The effectiveness of fungi againstinsect pests depends on many factors: having the correct fungal species with thesusceptible insect life stage, at the appropriate humidity, soil texture (to reach grounddwellinginsects), and temperature. The fungal spores which can be carried by windor water, must contact the pest insect to cause infection. When insect-pathogenicfungi are applied, for example through a spore-solution, good spray coverage of theplants is essential.caterpillar wilt129 Cabbage Ecological Guide - 2000

Major Natural Enemies of Cabbage Insect PestsConservationMany insect-pathogenic fungi live in the soil. There is evidence that application of some soil insecticides,fungicides and herbicides can inhibit or kill these fungi. For example, even very low concentrations ofsome herbicides can severely limit the germination and growth of Beauveria bassiana fungal spores insoil samples.6.3.3 VirusesBaculoviruses are pathogens that attack insects and other arthropods. Like somehuman viruses, they are usually extremely small (less than a thousandth of a millimeteracross), so they can only be seen with powerful electron or light microscopes.There are two main types of Baculoviruses, important for insect pest control:· Nuclear polyhedrosis virus (NPV) has been successfully controlling several caterpillar pests ofvegetables including cabbage butterflies, diamondback moth (Plutella xylostella), cabbage looper(Plusia sp.), armyworms (Spodoptera sp.), bollworm (Helicoverpa armigera), and European cornborer (Ostrinia nubilalis).· Granulosis virus (GV): have been found in several caterpillar species including diamondback moth(Plutella xylostella), cabbage butterflies (Pieris sp.), cabbage looper (Plusia sp.), cutworm (Agrotissp.), armyworms (Spodoptera sp.), and the webworm (Hellula undalis).Baculoviruses are composed primarily of double-stranded DNA. This is genetic material needed for virusestablishment and reproduction. Because this genetic material is easily destroyed by exposure to sunlightor by conditions in the host’s gut, infective baculovirus particles (virions) are protected by protein coatscalled “polyhedra” in NPVs, and “granules” in GVs. The protective coating allows the virus to exist in theopen air, outside the host’s body. It can only multiply inside a host.The majority of baculoviruses used as biological control agents are in the genus NPV .There are different strains (or “varieties”) of NPV and they are commonly present at low levels in manyinsect populations. Virus strains are usually specified with a letter-combination. For example:SeNPVNPV for control of armyworm Spodoptera exiguaSlNPVNPV for control of armyworm Spodoptera lituraHaNPVNPV for control of bollworm Helicoverpa armigeraControl of Spodoptera exigua by SeNPV: a success story from Indonesia.Spodoptera exigua is the major constraint to shallot production in several areas in Indonesia.Experiments were carried out under the Clemson Palawija IPM project with the Institut PertanianBogor in order to assess the SeNPV’s potential at different S. exigua population levels, as comparedto insecticides. Treatments included: SeNPV, SeNPV + hand picking larvae, hand picking larvae (noSeNPV) and control. Those involving insecticides included: Insecticide treatment, insecticides +hand picking, hand picking alone, and control.SeNPV and SeNPV along with hand picking larvae provided the best control of S.exigua. Yields inthe untreated control plots were nearly zero. Plots with hand picking alone significantly improvedyields but highest yields were obtained when SeNPV was carried out with hand picking.Since this IPM project began, the use of SeNPV has been incorporated into the biocontrol program inWest Sumatra. It is estimated that over 10,000 farmers are currently using SeNPV for Spodopteraexigua control in shallots. Many farmers are producing NPV on-farm. Farmers are involved in theproduction, multiplication, and distribution of biopesticides (NPV as well as other biocontrol products)and training in their use. The production and use of the virus has become an essential part of TOT andFFS training with idea of helping to stabilize the shallot ecosystem and let other natural enemiescolonize the crop. Farmer training is the key to the long term stability of the program (Shepard, 2000).Cabbage Ecological Guide - 2000130

Major Natural Enemies of Cabbage Insect PestsInsect viruses are not harmful for humans, animals, predators and adult parasitoids. Larval parasitoidsthat are still developing inside an insect are affected when the host insect dies due to viral infection.Mode of action and symptomsInsect viruses must be eaten by an insect to cause infection. They may also be spread from insect toinsect during mating or egg laying. In some cases, for example while searching for suitable hosts for egglaying, beneficial insects such as parasitoids may physically spread a virus through the pest population.An example is the parasitoid Cotesia sp. that can spread granulosis virus in Pieris rapae (ref. www16).Viruses enter an insect’s body through the gut. They replicate in many tissues inside the insect andinterfere with the feeding, egg laying and movements of the insect.Different viruses cause different symptoms. NPV-infected larvae may initially turn white and speckled orvery dark. Some may climb to the top of the plant, stop feeding, become limb and hang from the upperleaves or stems (“caterpillar wilt” or “tree top disease”).Insects infected with a granulosis virus (GV) may turn milky white and stop feeding. In both cases, thebody contents of the dead larvae are liquid and the skin of the insect breaks easily to release theinfectious virus parts. Death from a virus infection occurs within 3 to 8 days.EffectivenessA virus infection, either naturally occurring or applied, can seriously reduce a pest population, especiallywhen the pest population is high. Infected insects fall apart on foliage, releasing more virus. This additionalinfective material can infect more insects. Transmission of the virus through the population may takedays or weeks but, if conditions are suitable, the entire population may eventually collapse. See also boxabove.Advantages and disadvantages of NPV are indicated in table 6.3.3Table 6.3.3 : Advantages and disadvantages of NPVNPV - AdvantagesNPV - DisadvantagesHost specificEasily produced (if live hosts are available)Symptoms easily recognized in the fieldSafeMay recycle in the field (e.g. spread throughpopulations in the field)Easy to apply and evaluateHost specificSlow actingBreaks down by sunlight (becomes inactive)Large sized larvae not affectedRequires living host to produceNeeds proper storing (cool and dark)(modified from FAO Dalat report (Carner&Shepard), 1998)Conservation and productionFor viruses that occur naturally, conservation is not an issue because the circumstances in which theviruses occur can usually not be influenced very much. Naturally occurring viruses, as well as virus131 Cabbage Ecological Guide - 2000

Major Natural Enemies of Cabbage Insect Pestscultures from laboratories or commercial sources, can be multiplied on-farm. Both in Vietnam and IndonesiaNPV is locally reproduced by IPM farmers with mixed results. Quality control issues remain an importantaspect of on-farm reproduction of NPV. See box below.NPV production on-farm: some quality mattersIt was noted that when NPV was multiplied on-farm the virulence of the NPV solution could vary fromone season to the next. In fact, an NPV highly effective in controlling e.g. Spodoptera sp. in oneseason could give low control in the next season, when diseased caterpillars were used to make anew NPV solution. A number of issues may contribute to this:· When wild insects (from the field) are used to prepare NPV solutions, it can be difficult to distinguishlarvae of susceptible and non-susceptible species. For example, In India and Thailand, larvae ofH. armigera, Spodoptera exigua and Spodoptera litura can occur together and at the third instar,when inoculation is most effective, they are difficult for untrained observers to distinguish. Mixingdifferent insect species reduces the viability of any one NPV strain.· Wild larvae can themselves be carrying pathogens that may enter the production system andcompete with the NPV. For example, microsporidea and Bacillus sp. can be difficult to distinguishfrom NPV unless staff are well trained. Co-infection with other pathogens may reduce the “yield”of NPV.· When fresh leaves are used to feed the larvae, these leaves may also be contaminated withunwanted entomopathogens. These pathogens can reduce NPV production.· When healthy larvae are inoculated, it is important to infect insects at the right stage. Optimizingthe age/weight at infection is crucial to maximizing productivity in individual insects. Also, lastinstar caterpillars are usually unaffected by NPV.Strict quality control procedures are not only essential for product consistency, but also for safety.Where quality control is inadequate, microbial contamination of the final product is inevitable. Inmost of these cases this will merely lead to a loss of efficacy due to dilution of the active ingredientby competing microorganisms. However, it is possible that potential human pathogens may alsocontaminate these production systems. Quantification of the degree of contamination and identificationof these contaminants is important in determining the likely risk to human health. Many low technologyproduction systems (such as many on-farm NPV production areas) in use around the world haveminimal or no quality control procedures. This is an unsatisfactory situation and can damage thereputation of microbial control in addition to posing a serious health risk to those who produce orcome into contact with the product (Jenkins & Grzywacz, 1999).6.3.4 NematodesThere are many species of nematodes (very small worms). Some of them, likerootknot nematodes, attack and damage plants. Other nematode species arebeneficial in that they attack pest insects that live in the soil or that spend sometime of their life cycle in the soil such as beetle larvae, cutworms, and somearmyworms. These nematodes are called entomopathogenic nematodes.Nematodes have life cycles like insects: they usually mate, lay eggs, and there are several larval stages.Yet, they are often lumped with pathogens and not with insects, presumably because of their symbioticrelationship with bacteria, and because the symptoms they cause look like disease symptoms.Many species of naturally occurring, beneficial nematodes live in the soil and on plant material. The roleCabbage Ecological Guide - 2000132

Major Natural Enemies of Cabbage Insect Pestsof many of these species is not well known, but some nematode species have received attention aspotential biological control agents. Some of these nematodes can be mass produced and are availablecommercially in some countries. These beneficial nematodes do not harm plants, animals and mostbeneficial insects.The main species of beneficial nematodes include:· Steinernema species (previously called Neoaplectana): There are several species of this nematodeand all of them have a very broad host range. Different Steinernema species carry different strains ofa bacteria. Two important members of Steinernema are (D’Amico, www14):1. Steinernema riobravis - potential against eggplant fruit and shoot borer (Leucinodes orbonalis).Its host range runs across multiple insect orders. It can be effective against insects such ascorn earworm (Helicoverpa sp.) and mole crickets. This is a high temperature nematode, effectiveat killing insects at soil temperatures above 35°C.2. Steinernema carpocapsae - effective against lepidopterous larvae, including cutworms (Agrotissp.), armyworms (Spodoptera sp.), and some other insects.Important attributes of S. carpocapsae include ease of mass production and ability to formulatein a state that allows several months of storage under refrigerated conditions.Steinernema carpocapsae is recommended by the Dept. of Agr. Extension of Thailand againstwebworm Hellula undalis and fleabeetle Phyllotreta sp. (larvae live in the soil). The species S.riobravis is more heat tolerant than S. carpocapsae and does not need to be stored in therefrigerator.· Heterorhabditis species: carries a different species bacteria than Steinernema nematodes but entersand kills insects in a similar way. These nematodes also enter insects through their skins as well asthrough natural openings. They have a slightly longer life cycle than Steinernema species and alsoa broad host range.Mode of action and symptomsNematodes actively search for suitable hosts,often attracted by the carbon dioxide (CO 2)emitted by their prey. The third stage nematodelarvae are the infectious stage and only thesecan survive outside the host insect because theydo not require food. The nematodes carry insectpathogenicbacteria inside their gut. Differentnematode species carry different species ofbacteria. Once the nematode penetrates its host,usually through an available opening in the skinof the insect, the bacteria multiply and kill theinsect. The nematodes feed on the bacteria andon the insect tissue, then mate and reproduce.After 6 to 10 days, young nematodes emergefrom the dead insect to seek out and colonizenew hosts.reproductionrelease of nematodessearch for new hostsmatingnematodes enter the insect(modified from Hoffmann et al, 1993)release of bacterialhost diesAffected insects usually die within 1 or 2 days.Those killed by Steinernema species turn brown-yellow in color from the bacterial infection. The insectsare very soft, and easily crack. Insects killed by Heterorhabditis nematodes become red and gummy.133 Cabbage Ecological Guide - 2000

Major Natural Enemies of Cabbage Insect PestsEffectivenessInsect-attacking nematodes are best suited for use against pest insects that spend some or most oftheir life cycle in the soil or in moist, protected places (like inside shoots and fruits). However, nematodesare often not effective against insects feeding on open foliage because they quickly lose effectiveness indry conditions. Nematodes can travel in the soil over considerable distances and actively seek their preyif temperature and humidity are correct.As with most biological control agents, to use insect-pathogenic nematodes effectively, it is also necessaryto understand the life-cycle of the pest insect to ensure that the most susceptible life stage is targeted.Many vegetable insect pests are susceptible to attack by nematodes but for many, the potential ofnematodes for field control still needs to be evaluated.Nematodes can be cultured in living hosts and in artificial media with little chance for contamination.Several species of nematodes are now commercially available. See “The Biopesticide Manual” andinternet sites such as www25 and www29 (chapter 12, Reference list).soil particlesNematodemovementthrough soilnematode movement through soilNematode solutions, when obtained from elsewhere, can be stored in the refrigerator for a short time afterarrival because the nematodes are in a dormant state. Before applying the nematodes, this dormancymust be broken by stirring them in room temperature (over 18 o C) water to provide oxygen. After dormancyis broken, they must be used immediately. They prefer a moist soil and are damaged by light and soshould be applied in the evening. Beneficial nematodes move faster in sandy soil than clay.ConservationGuidelines for conserving native entomopathogenic nematodes have not been well documented. In general,nematodes (both when indigenous and when applied as a spray) need protection from the drying radiationof the sun and from extremes of temperature. Although they need a moist environment to stay alive andmove around, they can form a “resting stage” to survive adverse conditions.6.4 Other natural enemies6.4.1 BirdsThe value of wild birds as insect predators is clearlydemonstrated in many situations. In some areas in India,bird perches are placed in vegetable fields to provide a restingplace where birds can lookout for food like caterpillars!Farmers in various countries have been using chickens incotton plots to eat the cotton stainers and other bugs thatBirds: insect predatorsCabbage Ecological Guide - 2000134

Major Natural Enemies of Cabbage Insect Pestsdrop to the ground when disturbed. Chickens also eat various caterpillars and pupa that are on theground.In several parts of South East Asia ducks have been effectively used against golden apple snails in rice.6.4.2 PigsSometimes, pigs are allowed to spend some time at the vegetable field afterharvest. This is to the advantage of both farmer and pig because the pigs will eata large part of crop debris and may also dig into the soil in search for pupae ofinsects. When eating crop left-overs, possible diseases and insect larvae andeggs that are still present on the old leaves, are removed and cannot spread tothe next crop. An exception is clubroot in cabbage: this root disease can toleratepassage through the intestines of farm animals.Natural enemies are very valuable :they help farmers to control pests!135 Cabbage Ecological Guide - 2000

Disease Ecology7DISEASE ECOLOGYSUMMARYDisease ecology studies pathogens that cause plant diseases in relation to theirenvironment.Cabbage diseases are caused by pathogens such as fungi, bacteria, viruses andnematodes.Most pathogens spread attached to or inside seeds, or infected plant material, orare carried with wind, water (rain, irrigation water, ground water), through insectsand by humans or animals (attached to cloth or skin, and transported with plants/harvested crops).A disease is the result of interactions between a pathogen, a host plant and theenvironment. These interactions are shown in the disease triangle.pathogenenvironmenthostPathogens can infect a plant when 1) the variety of that plant is susceptible to thedisease, 2) the disease is present and virulent (able to infect the plant), 3) theenvironment (e.g. humidity, temperature) is favorable for the disease to develop.Disease management is focused on changing or influencing one of these threeelements to prevent the disease from attacking the plant. Studying disease in thefield, or setting up field experiments is an excellent way of finding out if symptomsare caused by a disease and how some (environmental) factors influence diseasedevelopment. Knowing characteristics of a disease will give you clues on how tomanage it!Available fungicides and bactericides are often not effective enough to stop anyof the major cabbage diseases, especially during prolonged periods of wetweather. If at all necessary, fungicides should be combined with structural managementmethods like adding organic material to the soil (compost), crop rotation,sanitation, etc.The antagonistic fungi Trichoderma sp. have become widely available in manycountries in South East Asia. Trichoderma sp. can suppress several soil-borneplant pathogens in vegetables. More biological agents may become available forcontrol of plant diseases in the future.Cabbage Ecological Guide - 2000136

Disease Ecology7.1 Plant diseases and pathogensDiseases are an important part of crop protection, but they are usually verydifficult to understand in the field. This is partly because the causal organismsare very small and cannot be seen moving around like insects. You can onlyrecognize diseases by their symptoms which vary from dwarfing of the plant,color changes, leaf spots and necrosis to wilting, (root) malformations androtting.Plant diseases are caused by living (biotic) organisms, called pathogens. Main pathogens of plants arefungi, bacteria, viruses, and nematodes. Some characteristics of pathogens are listed in the box below.Fungi, bacteria, viruses, and nematodes (and other organisms such as mycoplasmas) are often lumpedtogether under the term microorganisms. Only very few microorganisms may cause injury to the cropunder certain circumstances. Most of them are beneficial: they may be decomposers which play animportant role in the nutrient cycle. Several microorganisms are true “natural enemies”. Well-knownexamples are the bacterium Bacillus thuringiensis (Bt) and the virus NPV, which can control several pestinsects of vegetables. Likewise, there are fungi that control pest insects like aphids or caterpillars.Insect-pathogens are described in section 6.3.Some fungi can infect, attack or work against (antagonize) other fungi that cause plant diseases. Theyare called antagonists, the natural enemies of plant diseases, and also friends of the farmer! A wellknownantagonist is the fungus Trichoderma sp. which can reduce damping-off disease in nurseries(section 7.10.1).PATHOGENSFungi are plants that feed on other organisms, living or dead. There aremany different types of fungi: some are living in the soil breaking up deadplant parts, others feed on living plants and cause wilts and other diseases.Most fungi grow with tiny threads called mycelium and for their reproductionthey produce spores that serve as seeds. Sometimes a powdery mat thatcovers the diseased parts of a plant can be seen. This mat is composed ofmillions of spore producing structures of the fungus.Bacteria are very small organisms and can only be seen through a microscope.Few bacteria affect plants. Bacteria can cause both rotting of plants,wilting, and leaf spots. Bacteria do not form spores like fungi. They often multiplythrough cell division (splitting themselves into two). Some bacteria cansurvive for a long time by surrounding themselves with a protective coatingwhich prevents them from drying out. Bacteria grow in wet conditions.Viruses are even smaller than bacteria. They can only be seen with a powerful electron microscope.Viruses exist in living cells and cannot live outside a plant or an insectvector. Virus diseases may take a long time to recognize as often the onlyeffect on the crop is a gradual loss of vigor. Symptoms often depend onenvironmental conditions such as temperature. Plants are small, may bestunted and yields are lower. Sometimes the signs are more obvious whenred or yellow streaks appear on the leaves (mosaic). Still it is often difficultto distinguish a viral disease from a mineral deficiency. Viruses can infectnew plants through seeds or seed tubers, direct contact between plants or indirectly through vectors.The main vectors for plant viruses are sucking insects like aphids, plant hoppers and whiteflies.137 Cabbage Ecological Guide - 2000

Disease EcologyNematodes are very little worms (about 1 mm long) which usually arepresent in large numbers in the soil. Nematodes have life cycles like insects:they usually mate, lay eggs, and there are several larval stages.Yet, they are lumped with pathogens and not with insects, presumablybecause of their symbiotic relationship with bacteria (see section 6.3.4). Inaddition, symptoms caused by nematodes are often hard to distinguish from other diseases. Somenematode species can cause damage by sucking plant roots. In some cases, roots may form gallsdue to nematode attack (rootknot nematodes). Some nematode species are damaging becausethey transmit viruses. Other nematodes may be beneficial because they attack pest insect species.Plant diseases can also be caused by non-living (abiotic) agents. These are called physiological disordersrather than diseases. Symptoms of physiological disorders include discoloration of leaves throughdeficiency or excess of a certain fertilizer, symptoms from sun burn or pesticide burn. It is often hard totell the difference between a disease and a physiological disorder. Some guiding questions on factorscausing disease-like symptoms on plants are listed in section 7.6.7.2 How pathogens grow and multiplyPathogens have different ways of growing in or on a host plant.Fungi usually form mycelia, thread-like structures comparable to branches of plants. Some fungi live ontop of the plant tissue and have small “roots” (haustoria) in the plant that take food from the plant cells tofeed the fungus (example: powdery mildew on peas: you can see it as a white downy mould on theupperside of leaves). Others live inside the plant and may even use the plant vessels to spread throughthe plant (for example black rot in cabbage: the veins turn black due to the bacterium infection). Bacteriaand viruses almost always live inside the plant only. Nematodes often have one or more life stages insidea host plant but may also be free-living in the soil.Fungi have two general ways of reproduction :Vegetative reproduction: parts of the fungi, e.g. pieces of mycelium, that can develop further when placedin a suitable environment.Reproduction by spores: spores are like “seeds” of a fungus: when they land at a suitable place theygerminate and the fungus grows from there. Under suitable conditions the fungus may produce sporesagain. When conditions are not favorable, the fungus may develop a resting stage, which will settle ondebris or in the soil, or it may form resting spores that can survive adverse conditions such as drought.Clubroot in cabbage is a fungus which can produce resting spores that can remain active in the soilwithout plants for over 10 years!Bacteria usually multiply by cell division: the bacterium cell gets larger and splits into two. This can govery fast! For example E. coli bacteria, under favorable conditions, may double every 20 minutes! Thatmeans that starting with one bacterium, there are over 4000 of them in about 4 hours. Usually, lack offood or accumulation of waste products prevents this high speed multiplication from happening.Some bacteria can survive for a long time by surrounding themselves with a protective layer whichprevents them from drying out.Viruses exist in living cells of a plant. Multiplication of viruses is very complex. When a virus has entereda plant cell, it falls apart into specific molecules which “take over” the plant cell. Instead of producingplant tissue, the cell now produces more virus parts.Nematodes are little worms that have life cycles like insects: they usually mate, lay eggs, and there areseveral larval stages. Some of these larval stages can travel through the soil in search of new host plants.Cabbage Ecological Guide - 2000138

Disease Ecology7.3 How diseases spreadDiseases can spread from one plant to the other, but also from one field to the next and even one locationto another. A few general ways in which pathogens can spread are described here.Direct transmission through:· Seed: pathogens can be carried on or inside a plant seed.· Vegetative plant parts: infected transplants may carry diseases from nursery to the main field; similarlydiseases can be transmitted by infected tubers, cuttings, runners, grafts, etc.Indirect transmission through:· Growth of the pathogen: pathogens can spread over short distances by growth of the mycelium. Forexample wood rotting fungi can spread through the soil from one tree or trunk to the next by activegrowth.· Wind: fungi which produce spores on the surface of plants can be disseminated by wind. Examplesare mildew (both powdery and downy mildew), Alternaria leaf spot, black leg (Phoma lingam). Thereare examples of spores such as grain rust (Puccinia graminis) that have been found over 4000 mabove an infected field! Often wind blows the spores over certain distances and rain may deposit thespores down. Some bacteria can also be dispersed by wind.· Water: flood or irrigation water may carry pathogens or spores, especially those in or near soil. Thesplashing of water during rain or heavy dews can spread spores and bacteria to plant parts near thesoil or to different parts of the same plant or to neighboring plants. Examples of water-carried pathogensare black rot bacterium (Xanthomonas campestris): the secondary spread from initial infectionresults largely from splashing during rains. Clubroot (Plasmodiophora brassicae) is spread by surfacewater. Water however is not as important as wind for long distance dissemination.· Soil: soil can contain infected plant debris and it contains spores of fungi such as damping-off (e.g.Pythium sp.) and clubroot (Plasmodiophora brassicae) and bacteria such as black rot (Xanthomonascampestris). Soil can be a reservoir of diseases which are spread when soil particles are transported,for example attached to seedling roots or attached to tools or shoes of man.Survival and spread of soil-borne pathogensSoil-borne pathogens can survive on or in a host plant (including weeds), some survive on dead hostplant tissue or on dead organic material, some form resting spores or latent stages (such as thickwalledbacteria or fungus spores to survive in adverse conditions). Root nematodes survive as eggs(egg cysts) or as adults.Soil-borne pathogens can be spread by wind, water, vectors or humans and carried with soil particles.An example: Pythium sp. causes damping-off disease in seedlings. Dying seedlings contain thespore-carrying structures of the fungus. The spores can drop to the soil (and attack seeds or youngseedling roots), or be carried by wind or spread by surface water or irrigation water to anotherlocation. Pythium can be transported attached with soil to the seedling roots during transplanting.And Pythium can form thick-walled spores (called oospores) that can survive during adverse conditionsand persist for several years in the soil.· Insects, mites, nematodes: dissemination of pathogens can occur incidentally when e.g. sporesstick to the body of an insect or mite going from one plant to another. More important is in case ofinsects when an insect becomes a vector and carries and transmits a pathogen (often important incase of virus diseases) from one host plant to another. Most vectors are sucking insects such asaphids, whiteflies and leaf hoppers.139 Cabbage Ecological Guide - 2000

Disease EcologyNematodes can also be transmitters of pathogens. In case of vegetables, it is also likely that nematodescreate entry points for bacteria and fungi by making wounds in roots.· Humans, animals: spread of pathogens occurs in two ways: through the person, tools or animalsand through the objects that are transported. Persons and animals spread diseases by walking andworking in fields with infected plants, spreading sporessticking to the body but also causing small injuries toplants (e.g. during transplanting or field work) whichcan be entry points for pathogens. Longer distancedissemination by man is usually done by transportingdiseased planting materials or infected soil particles.7.4 How pathogens attack a plantA spore of a fungus or a piece of the mycelium (the “body” of the fungus) can penetrate a host plant. Itcan enter a plant through wounds in the plant tissue, through fine root hairs, through natural openings likestomata (the “breathing cells” of a plant) or it can actively penetrate the tissue of the plant. To do this,some fungi produce special chemicals (enzymes) that damage the plant tissue and allow the fungus toenter.Bacteria cannot actively penetrate plants and need woundsor natural openings to enter.A virus needs a wound to enter, either a mechanical woundor a wound created by an insect. Most nematode species,such as rootknot nematode, can actively penetrate plants.The differences in the ways of attacking a plant may be thereason that you sometimes see all plants in a field infectedwith a disease (for example leafspot can be present on allplants because it can actively penetrate the plant tissue)whereas another disease may only be visible on a few plants (for example softrot: it needs a wound toenter the plant).The infection process by some pathogens can be very quick. Damping-off in seedbeds for example, cankill seedlings in less than a day! That will usually be too short to even notice disease symptoms! Othersjust parasitize on a plant and do not cause the death of the plant - like leafspot on cabbage: it can reducethe yield but plants will survive.7.5 When can a pathogen attack a plant?A disease is the result of interactions between a pathogen, a host plant and the environment. Theseinteractions are shown in the disease triangle:pathogenenvironmenthost plantCabbage Ecological Guide - 2000140

Disease EcologyThe disease triangle says that a plant will get infected with a disease when:· the variety of that plant is susceptible to the disease,· the disease is present and virulent (able to infect the plant),· the environment (e.g. humidity, temperature) is favorable for the disease to develop.Disease management is focused on changing or influencing one of the three elements of the triangle toprevent the disease from attacking the plant. A few examples:Changing the host plant can be: not growing a host plant, e.g. by crop rotation, or using a resistant variety.Changing the presence of the pathogen can be: removing leaves with the spores of the disease from thefield before planting a new crop so that the disease cannot infect the new plants from the leaves that wereleft in the field after harvest (sanitation).Changing the environment can be: using furrow irrigation rather than overhead irrigation so that the leaveswill not get wet. Humidity stimulates spore formation (e.g. leafspot in cabbage) and spread of the disease.Creation of a disease triangle in a workshop on management of soil-borne diseases, HaiPhong, Vietnam (1999)Participants of this workshop, mainly IPM trainers, discussed about disease development, with theobjective to develop studies (Participatory Action Research) with IPM farmers on disease management.One of the diseases selected to prepare a disease triangle was bottom rot (Rhizoctoniasolani) in cabbage. The following management methods for bottom rot resulted from the discussions:PATHOGEN· Practicing proper field sanitation (X)· Using compost (to improve soil structure, increase soil nutrients,reduce soil-borne pathogens, strengthening activities of beneficialorganisms) (X)· Using clean water resource· Uprooting diseased plants for composting (X)· Applying good irrigation methods· Using Trichoderma· Practicing crop rotationHOST PLANT· Using less susceptible variety (incl.non-diseased seedlings and healthyplants) (X)· Applying fertilizer properly (X)· Keeping sufficient moisture (X)· Practicing proper crop timing (X)· Practicing crop rotation (X)· Prepare field carefully· Make high beds for good drainage· Buying varieties from reliable shopENVIRONMENT· Practicing proper crop timing (X)· Applying compost (X)· Using proper transplanting density· Not flooding furrows· Proper weed control· Applying lime (X)(X) = done by all Vietnamese farmers (according to workshop participants).(FAO Workshop on PAR on management of soil-borne diseases, 1999)141 Cabbage Ecological Guide - 2000

Disease Ecology7.6 A disease or not a disease...? How to find out!Very often, it is difficult to tell if a brown orblack spot on the leaf or a piece of dead leafis actually a disease or just a little insectdamage or mechanical damage. Sometimesthe symptoms of diseases are not very clear,or a different environment or climate makesa symptom look slightly different from the“theoretical” symptoms.It is important to find out because if a spotor a discoloration is actually a disease, youmay still be able to do something to preventit from spreading into the rest of the field.This can be uprooting the diseased plants.For some diseases you may have to spray a fungicide to stop the spread. It is important to train yourselfin recognizing early symptoms of a disease. If you can see the first symptoms of a disease early, theremay still be time to prevent it from reaching a damaging level of infestation.Often with some common sense and a thorough knowledge of a field’s recent history, it is possible to findthe cause for specific plant symptoms. The following are guidelines that may be useful in diagnosingvegetable problems (ref. modified from www21).Guidelines for diagnosing vegetable problems1. Identify the symptoms. Do the leaves have a different color? Do leaves or the whole plant have adifferent appearance, e.g. smaller size leaves or bushy plants? Are there any leaf spots or spots onthe stems or fruits? Wilting of shoots or of the whole plant? Holes in the leaves or in the stem? Rootabnormalities? Fruit rot?2. Are all plants in the field affected? Are small areas in a field affected? Or individual plants?3. Determine if there is a pattern to the symptoms. Are affected plants growing in a low spot of the field,poor drainage area, or an area with obviously compacted soil? Does the pattern correlate with currentfield operations?4. Trace the problem’s history.· When were symptoms first noticed?· What rates of fertilizer and lime were used?· What pesticides were used?· What were the weather conditions like before you noticed the problems - cool or warm, wet ordry, windy, cloudy, sunny?5. Examine the plant carefully to determine if the problem may be caused by insects, diseases ormanagement practices.Insects: look for their presence or feeding signs on leaves, stems and roots. Sometimes it’s easierto find insects early in the morning or toward evening.Diseases: look for dead areas on roots, leaves, stems and flowers. Are the plants wilting eventhough soil moisture is plentiful? Then check the roots for root rot symptoms or root deformations.Are the leaves spotted or yellowed? Are there any signs of bacterial or fungal growth (soft rots,mildew, spores, etc.)? Look for virus symptoms-are the plants stunted or do they have obviousCabbage Ecological Guide - 2000142

Disease Ecologygrowth malformations? Are all the plants showing symptoms, or are just a few scattered around thefield?6. Could there be nutritional problems? The box below lists a number of characteristic deficiencysymptoms for the major and minor nutrients.7. Could there be a nutrient toxicity? Boron, zinc, and manganese may be a problem here. Soluble saltinjury may be seen as wilting of the plant even when the soil is wet. Burning of the leaf margins isusually from excessive fertilizer.8. Could soil problems be to blame? Soil problems such as compaction and poor drainage can severelystunt plants.9. Could pesticide injury be at fault? Pesticide injury is usually uniform in the area or shows definitepatterns. Insecticides cause burning or stunting. Herbicides cause burning or abnormal growth.10. Could the damage be caused by environmental conditions? High or low temperatures, excessivelywet or dry, frost or wind damage, or even air pollution? Ozone levels may rise as hot, humid weathersettles in for long stretches. Look for irregularly shaped spots which may look similar to feeding ofmites and certain leafhoppers. Ozone flecks are usually concentrated in specific areas of the leaf,while feeding damage from insects is spread uniformly across the leaf.Deficiency symptoms for major and minor nutrients:· Nitrogen: Light green or yellow older foliage.· Phosphorus: Stunted plants and purplish leaves.· Potassium: Brown leaf margins and leaf curling.· Calcium: Stunted plants, stubby roots. (Causes blossom end rot of tomatoes, tip burn of cabbage,celery blackheart, and carrot cavity spot).)· Magnesium: Yellowing between veins of older leaves.· Sulphur: Yellowing of new leaves, stunted plants.· Boron: Growing points die back and leaves are distorted.· Copper: Yellowing of leaves which become thin and elongated, causes soft onion bulb with thinscales.· Iron: Light green or yellow foliage on youngest leaves.· Zinc: Rust-colored spots on seed leaves of beans, green and yellow striping of corn, yellowing ofbeet leaves.· Manganese: Mottledyellow areaappearing on youngerleaves first. In beets,foliage becomesdeeply red.· Molybdenum:Distorted, narrowleaves, someyellowing of olderleaves; whiptail leafsymptoms inMolybdenum deficiency symptoms in cauliflowercauliflower.143 Cabbage Ecological Guide - 2000

Disease Ecology7.7 Studying diseasesWhen despite checking the guidingquestions from the section above, it isstill unclear if something is a disease,an option would be to observe thesymptoms in the field or in a ‘classroom’,or house over a period of time. In someTOTs, this is an experiment calleddisease zoo, disease observatorium ordisease culture. An example for leafspots is given below.Disease zoo for leaf spots:Select one or a few plants in the field that have disease-likesymptoms. Mark the plants with a stick and label the leaves thatshow the symptoms (you can put a tag on the leaf or draw a bigcircle with a waterproof markerpen around the spot you want tostudy). With cabbage it is also possible to take some leaves offthe plant and place them in a plastic bag, a glass jar, or in a vasefilled with water. Draw the leaves with symptoms in detail (usehand lens) using color pencils (what color is the symptom, whereis it located, do you see structures inside the symptom (e.g. blackspecks), what color is the plant tissue around the symptom, etc.).Measure the size of the symptom and note it down with yourdrawing. Also note down if it is a young or an old leaf and if theplant was located in the middle or more towards the border of the field.monitoringareasRepeat the above after a few days: draw and measure the symptoms. If you find that the symptomsare growing, becoming bigger in size and maybe even have spores (you can sometimes find them asdusty powder or in small black pustules on the spot) it is very likely that you are looking at a disease.Check the symptoms found with the table in chapter 11, key tables and with details on some of themajor diseases of cabbage to confirm diagnosis. Leaves taken off the plant do not last longer thanabout 5 days.Related exercises from CABI Bioscience/FAO Manual:3.1. Description of disease symptoms3.2. Identification of disease symptoms3.3. Disease collection3.4. Pathogen groups3.8. Pathogen groups name game3.9. Cultivating a fungusCabbage Ecological Guide - 2000144

Disease Ecology7.8 Control or management?It is important to realize that diseases require another way of thinking in order to have long-term control.Diseases must be managed, not controlled. But what is the difference and why is that important toknow?Management means a range of activities that support each other. Many or these activities should bedone before transplanting of the crop, some even before sowing the seeds. Disease management is along-term activity, sometimes it is a planning for several years. It is mainly focused on preventing thedisease from coming into a field. It also aims at keeping disease pressure low in case a disease ispresent. Management usually needs the cooperation of several farmers working together to reduce overalldiseases in an area.Control is a short-term activity, focused on killing a disease or stopping the spread of it. The trouble withdiseases is that you only see them when you see the symptoms. That means infection already occurredat least a few days before. It also means that plants that look healthy today, may have disease symptomstomorrow. Once a plant is infected, it is difficult to actually kill the pathogen. Especially when pathogenslive in the soil and attack plants through the root system, they can only be controlled by proper managementtechniques like crop rotation or cultural methods. And those kind of methods usually have to bedone before transplanting the crop!Spraying fungicides, a typical short-term activity, may be a control option but only for a limited number ofdiseases and usually only partially. So a combination with cultural practices like sanitation is essential!It should be noted that some fungicides can kill natural enemies, including predators and parasitoids(see box in section 4.9).In order to make a good disease management decision, you have to know a few basic things about thedisease. Things like: where does it come from, how does it spread? Knowing this will give you a clue howto manage it. Soil-borne diseases are managed different from wind-borne diseases!Diseases can never be completely eradicated -but populations can be reduced to low levels!But before talking about control, think about: how important is this disease, what damage does it do tomy overall yield at the end of the season? What would be the effect of this disease to the crop in the nextseason? A few leafspots here and there may not reduce your yield. At what growth stage does thedisease appear? What are the weather conditions, are they favorable for a quick spread of the leafspot?Yes, you may be able to temporarily stop the spread of those leafspots by applying fungicides. But whatare the costs of those fungicides? What are the negative side-effects of fungicides to the natural enemypopulation? How much extra income do you estimate you can win by a few spotless cabbages? That iswhat counts in the end!7.9 Disease management: where to start?Disease management starts with the identification of the problem. Once you have found the cause of theproblem, and it is a disease, the easiest way is to check if there are any resistant crop varieties available(see section 3.2). Also, if you know that the disease is giving a lot of problems in one season but not inanother, it may be worth considering not to grow the crop in the susceptible season. Not growing the cropat all for a few years (crop rotation) is another often recommended practice in disease management,especially for soil-borne diseases (see section 3.12).145 Cabbage Ecological Guide - 2000

Disease EcologyWhen resistant varieties are not available, find out some more details on the disease. Start for examplewith: where does the disease come from? How does it spread?Knowing characteristics of a disease will give you clues on how to manage it !The table 7.9 below will summarize some sources and carriers for a number of important cabbagediseases.Table 7.9 : A summary of some sources and carriers for important cabbage diseasesDISEASEcontaminatedseedsotherinfectedplantsSOURCE(S) and/or CARRIER(S)diseasedcropresiduessoilcontaminatedwatercarriedby windcontaminatedtools, people,animalsdamping off - + + + + - +black rot + + + - + - +soft rot - + + - + - +Alternarialeafspot+ + + - - + +club root - + + + + - +downymildew- + + - - + +black leg + + + - + + +By checking the “+” symbols, you can see what the important sources and carriers for a disease maybe. Next thing is to see if these sources/carriers can be influenced. By eliminating or reducing a sourceor a carrier of pathogens, disease may be reduced! Some examples of management practices are listedbelow. This list is not exhaustive, check sections on individual diseases for a complete set ofmanagement practices.Cabbage Ecological Guide - 2000146

Disease Ecologycontaminated seeds : treat seeds before sowing (section 3.3),other infected plants : uprooting diseased plants, pruning infected leaves, increasing plant spacing,diseased crop residues : sanitation – removing all debris from previous crop from field,soil : crop rotation, for small areas: soil sterilization (sections 3.12 and 3.7.1),contaminated water : avoid planting down-hill of an infected field,carried by wind :cooperation with other farmers for sanitation practices, covering compostpiles, windbreaks (though usually of limited value),contaminated tools, clean tools, shoes, etc. when used in field, avoid working in the field whenpeople, animals, insects : plants are wet, control vector insects.Another factor to influence disease is the environment (see disease triangle, section 7.5). When youknow what environmental factors stimulate or inhibit the disease, you can sometimes influence these.Soil temperature may be influenced by mulching; humidity can be influenced by proper drainage of thefield, using furrow irrigation instead of overhead irrigation, etc.Even with all the knowledge, it remains a difficult task to manage diseases. When all preventive activitiesfail, there may not be another option than to use a fungicide. However, from an ecological and an economicalpoint of view, there is a lot to gain by setting up small experiments to test when and how to applyfungicides, to control diseases in your field, this season. Remember that natural enemies of insect pestand antagonistic organisms may also be harmed by fungicide sprays.Related exercises from CABI Bioscience/FAO manual:1.4. Effect of pesticides on spiders and other natural enemies3.6. Disease triangle to explain disease management3.7. Demonstration of spread of pathogens3.11. Simulating pathogen spread7.10 Antagonists: the Natural Enemies of pathogensNot only insects, but also plant pathogens have natural enemies. These are usually also fungi, bacteria,nematodes or viruses which can kill plant pathogens, reduce populations, or compete for nutrients orattachment to a host plant. Such microorganisms are called antagonists. Sometimes, the term“biofungicide” is used for antagonists.Antagonists of pathogens are not yet well understood. However, the research that has been done hasgiven promising results, and the study of antagonists has become a rapidly expanding field in plantpathology. The most “famous” antagonist in vegetable production is probably Trichoderma (see below)but others may be interesting as well. In Philippines for example, a fungus called Bioact strain 251, wasisolated from the soil which controls nematodes. Spore solutions of this fungus are now commerciallyavailable as “Bioact” (FAO Dalat report (V.Justo), 1998).147 Cabbage Ecological Guide - 2000

Disease EcologyAntagonists: how do they work…? Some examples:The fungus Gliocladium virens reduces a number of soil-borne diseases in three ways: it produces atoxin (gliotoxin) that kill plant pathogens, it also parasitizes them in addition to competing for nutrients.The biocontrol capacity of the fungus Trichoderma harzianum, recommended for control of severalsoil-borne pathogens, competes in the soil for nutrients with pathogens. Trichoderma fungi outcompetepathogens for nutrients and rhizosphere dominance (=area for a fungus to grow around the plantroots), thereby preventing or reducing the impact of pathogens.Others may compete for the entry place to the host plant, such as pathogenic and non-pathogenicFusarium sp. When a non-pathogenic organism blocks the entry, the pathogen cannot infect theplant.(Copping, The Biopesticide Manual, 1998)Antagonists have been applied to the above-ground parts of plants, to the soil (and roots), and to plantseeds. Under constant conditions, such as in greenhouses, antagonists can completely protect plantsfrom pathogens. In the field, disease control is likely to be more variable due to the varying environmentalconditions (mainly temperature, moisture, nutrient availability and pH).And, proper methods for the multiplication of antagonists as well as ways to formulate them need to befurther studied. However, some examples of successful field use of an antagonist are described below.7.10.1 Trichoderma speciesAn example of an antagonist that is widely available in South East Asia is Trichoderma sp. Trichodermasp. can suppress soil-borne plant pathogens, including those causing damping-off (Pythium sp.), root rot(Rhizoctonia solani), stem rot (Sclerotium rolfsii), and wilt (Verticillium dahlia) in vegetables. In addition,Trichoderma fungi often promote plant growth, maybe due to their role as decomposers. They may alsoaid in promoting soil fertility. In addition, Trichoderma sp. stimulates tissue development for example inpruned trees, through the enhancement of natural auxin release. Specific formulations containingTrichoderma are available to treat pruning wounds of fruit trees.Some Trichoderma species are:· Trichoderma harzianum – suitable for warm, tropical climates· Trichoderma parceramosum – suitable for warm, tropical climates· Trichoderma polysporum – suitable for cool climates· Trichoderma viride – suitable for cool climates and acid soils· Trichoderma hamatum – tolerant to excessive moisture· Trichoderma pseudokoningii – tolerant to excessive moistureTrichoderma harzianum and some others occur widely in nature. Isolates of e.g. Trichoderma harzianumwere selected for commercialization because of its ability to compete with plant pathogenic fungi. Thebeneficial fungi outcompete the pathogens for nutrients and for a place to grow around roots or in pruningwounds, thereby preventing or reducing the impact of pathogens.Gliocladium virens (previously known as Trichoderma virens) was the first antagonistic fungus to getapproval of the Environmental Protection Agency (EPA) in the USA for registration. Trichoderma is oftenused as a spore suspension on carrier material such as rice bran. It can be used both preventive andcurative. However, application before pathogens are visible, as a prevention, always gives the best control.Cabbage Ecological Guide - 2000148

Disease EcologyTrichoderma species are successfully used and multiplied in several countries in Asia, including Thailand,Philippines, Vietnam and Indonesia (FAO-ICP Progress report ’96 – ’99).Trichoderma sp. should be mixed into the soil a few days before (trans)planting.L A negative effect of Trichoderma has been reported on mushrooms. Trichodermacan negatively influence mushroom cultivation, possibly due to killing or inhibitingthe mushroom fungi. More research is needed to study these effects, but in themeantime it is advisable not to use Trichoderma close to a mushroom productionarea (Harman et al, 1998).Related exercises from CABI Bioscience/FAO manual:3.5. Beneficials among the pathogen groups7.11 What about fungicides...?Available fungicides and bactericides are often not effective enough to stop any of the major cabbagediseases, especially during prolonged periods of wet weather. Fungicides (if at all necessary) shouldalways be combined with structural management methods like crop rotation, sanitation, etc. (see section7.8).7.11.1 Chemical fungicidesThere are several ways of classifying fungicides. An often used classification is the following:· Preventive fungicides: those should be applied before the disease actually occurs. The fungicide willform a protective layer around the plant which prevents spores from germinating on the plant. Butagainst what diseases you should spray is often unclear and timing of fungicide application is verydifficult to predict. Also, when it rains, the fungicide will be washed off the leaves and there is noprotection anymore, just environmental pollution. There are products that can be added to the fungicidethat help it stick better to the plants, these are called stickers. Results in practice however vary.· Curative fungicides: products that you can spray when symptoms of a disease occur. Some of theseform a layer around the plant (contact products), others are uptaken by the plants and transportedthrough the veins to other plant parts (systemic products).Good toknow about fungicides:· There are few effective sprays against bacterial diseases!· There are no sprays against virus diseases! (usually insect vectors should be prevented fromentering the crop in areas where virus diseases are a problem).· Control of soil-borne diseases with fungicides is usually not effective: it depends on the pathogenhow deep below soil surface it can live and it is unclear how deep the fungicide will go. Somepathogens live inside plant debris in the soil, where they are protected from fungicides. From anenvironmental point of view, it is dangerous to apply fungicides to soil. What is the effect on thebeneficial microorganisms that decompose plant rests? Will the pesticide contaminate the groundwater? How long will the pesticide persist in the soil?149 Cabbage Ecological Guide - 2000

Disease Ecology· Frequent use of fungicides may lead to fungus resistance to that type of fungicide. That means thefungus is no longer susceptible to the fungicide. For example, there are different “strains” of Fusariumwilt in tomato (Fusarium oxysporum). All of these Fusarium strains cause tomato wilt but the geneticcharacteristics of a strain are slightly different. This is comparable with different varieties of tomato:all of them are tomato but they differ in e.g. fruit size, color and maturity. Strains may differ insusceptibility to fungicides.· Many fungicides can actually kill natural enemies of insect pests! For a study example, see box insection 4.9.¦Calendar sprayingThe application of pesticides at regular, fixed intervals during the season is known ascalendar spraying. This practice can be effective in disease control, but may lead to excessivefungicide use or poorly timed applications over the duration of the growing season, resulting in a lossof money for the farmer and environmental pollution. More important, calendar spraying is not basedon what is actually happening in the field, on agro-ecosystem analysis. It does not account forpresence of natural enemies, growth stage, weather conditions etc. Therefore, from an ecologicalpoint of view, calendar spraying should be discouraged.No recommendations for the use of specific fungicides will be given in this guide. The types, brands,doses of fungicides differ per country and local extension agencies or departments of agriculture mayhave national recommendation schedules.7.11.2 Botanical fungicidesNot much “scientific” information is available on the use of botanicals against fungal diseases. However,in practice farmers may use several botanical extracts to control diseases.Garlic is one the more commonly used botanicals, effective both as seed treatment for disease control(see section 3.3.3), and in a spray solution against fungal and bacterial diseases and insects. There aremany methods to prepare garlic sprays. One of them is listed below.Garlic spray: the recipeCrush many garlic cloves with a little water, then strain this and mix with water, 1 teaspoonof baking soda, and 2 or 3 drops of liquid soap. Test its effect as a preventive sprayagainst fungal and bacterial diseases and insects.Milk (not a botanical but of animal origin) can also have a function in preventing fungus and mainly virusdiseases in plants. No “official” trial data are available but milk is used a lot in greenhouses in for exampleNetherlands to dip cutting knifes during pruning of tomato. The milk protein inactivates viruses. Effectsson fungi are unclear. Milk is expensive for use on larger scale.Cabbage Ecological Guide - 2000150

Major Diseases of Cabbage8MAJORDISEASES OF CABBAGESUMMARYMajor diseases of cabbage in seedbeds are damping-off and downy mildew. In the mainfield, a number of other diseases can occur and cause yield loss which occasionally can besevere. Seldom will diseases in the main field cause total yield loss.Some general disease management practices are given here. Specific practices are listedunder individual disease sections.· Use of disease-resistant varieties. Cabbage varieties may vary in susceptibility to diseases.Check with seed companies and local extension offices for information. Setting upvariety trials to test how well particular varieties perform locally is recommended.· Increasing soil organic matter. This can increase soil microorganism activity, which lowerspopulation densities of pathogenic, soil-borne fungi.· Clean planting material. Use of clean seed such as treated seed (section 3.3) or “certified”seed that has been inspected for pathogens at all stages of production. Cleanplanting material includes healthy, disease-free transplants, also when bought from elsewhere.· Grow a healthy crop. A vigorous but balanced plant growth is the key! Fertilizer andwater management are important factors here. Some examples:v Fertilizer: using too much may result in salt damage to roots, opening the way forsecondary infections. Balancing watering and fertilizer is also important. The succulentgrowth of plants given too much water and nitrogen encourages certain pathogens.On the other hand, stressed plants, especially those low in potassium andcalcium, are more vulnerable to diseases.v water management: the most important practice is providing drainage to keep soilaround roots from becoming waterlogged to prevent rotting. It is also important thatfoliage stay dry. Infectious material or inoculum of water-borne pathogens spreadsfrom infected to healthy leaves by water droplets, and fungal pathogens need waterto germinate and enter the leaf. Water management methods are listed in section 3.9.· Sanitation. Removing diseased plants (or parts) will help prevent the spread of pathogensto healthy plants. Crop debris can be used to make compost. If temperatures duringcomposting rise high enough and are uniformly achieved in the pile by mixing, mostpathogensaredestroyed. Sanitation also includes weed control and insect control because manypathogens persist in weed hosts or are spread by insects.· Crop rotation. Rotate crops to disease-free fields to avoid buildup of pathogens in thefield. Rotation to an entirely different plant family is most effective against diseases thatattack only one crop. However, some pathogens, such as those causing damping-off androot rots, attack many families and in this case rotation is unlikely to reduce disease.· Use of biocontrol agents. Good results have been obtained with use of Trichoderma sp.for control of soil-borne diseases such as damping-off.151 Cabbage Ecological Guide - 2000

Major Diseases of Cabbage8.1 Damping-off in seedbeds (Fusarium, Rhizoctonia, Pythium, Phytophthora sp.)Causal agents : fungi – Fusarium, Rhizoctonia, Pythium, Phytophthora sp.A number of species of soil-dwelling fungi, including Fusarium, Rhizoctonia, Pythium and Phytophthorasp., infect vegetables, especially legumes, crucifers and solanaceous crops. Species of Pythium aremore common than the others. If the infection occurs either before (pre-emergence) or just after emergence(post-emergence), and development of a spot (lesion) at the soil line results in collapse andshriveling of the plant, the disease is called ‘damping-off’.Signs and symptomsInfection occurs just around the soil line in young seedlings. Damping-off fungi rarely attack transplantsin the field or established seedlings.The symptoms of this disease are brown, water-soaked areas around the lesion that shrivel and pinchthe seedling off at the base. The dry rot is usually limited to the outer part of the stem and infected plantsmay fall down or may remain more or less upright. Infected plants remain under-developed and usuallydie.Pre-emergence damping offStem rot(from Kerruish, 1994)Source and spreadThe fungi are natural soil inhabitants but when circumstances are favorable and when susceptible hostplants are present, the population can increase to damaging levels. It is difficult to predict when that willoccur: it depends on temperature and humidity but also on the population of microorganisms in the soil.Sometimes, there are microorganisms (antagonists) that serve as natural enemies of the pathogens:they can keep the population of the pathogen under control.Infection occurs through wounds or natural openings but Pythium can also actively penetrate the tendertissue near root tips.In case of Pythium infection, dying seedlings contain the spore-carrying structures of the fungus. Thespores can drop to the soil (and attack seed or young seedling roots), or be carried by wind or spread toanother location by surface water or irrigation water. Pythium can be transported in soil attached toseedling roots during transplanting. And Pythium can form thick-walled spores (called oospores) thatcan survive during adverse conditions and persist for several years in the soil.Cabbage Ecological Guide - 2000152

Major Diseases of CabbageRole of environmental factorsDamping-off occurs in areas with poor drainage or areas with a previous history of the disease. Dampingoffis often associated with high humidity and high temperature. The temperature range in which thesefungi can live is quite broad, from about 12 to 35 o C with an optimum (the temperature at which dampingoffdevelops fastest) of 32 o C. That is why you can find damping-off disease both in highlands with atemperate climate and in (sub)tropical lowlands.Disease cycle Phytophtora damping-off and root rot(from Kerruish et al., 1994)Natural enemies/antagonistsMany successes have been reported with the use of Trichoderma sp. for the prevention of damping-off.Trichoderma outcompetes fungi that cause damping-off for nutrients and a place to grow around the roots(“rhizosphere dominance”). There are several species of Trichoderma. The species Trichoderma harzianumhas been used successfully in tropical climates but Trichoderma parceramosum also gave good resultsin field trials in Philippines (FAO-ICP progress report ’96 – ’99). Trichoderma sp. are now available for useby farmers in, for example, Indonesia and Thailand. More details on Trichoderma in section 7.10.1.153 Cabbage Ecological Guide - 2000

Major Diseases of CabbageThere are several other antagonistic organisms that control damping-off fungi, such as Bacillus subtilis,Burkholderia cepacia, Pseudomonas fluorescens, Streptomyces griseoviridis, and Gliocladiumcatenulatum. Different strains of these antagonistic organisms have been registered in the United Statesas biocontrol products to control damping-off and some other soil-borne plant diseases. Examples arelisted in the table in section 8.4 on Rhizoctonia. To date, no information about use of these biocontrolproducts is available from Asia.Damping-off can also be reduced in soils rich in compost. Compost contains many different microorganismsthat either compete with pathogens for nutrients and/or produce certain substances (called antibiotics)that reduce pathogen survival and growth. Thus an active population of microorganisms in the soilor compost outcompetes pathogens and will often prevent disease. See section 3.5.3.1 on compost.Researchers have found that compost of almost any source can already reduce damping-off disease.The effect of compost on plant pathogens can be increased by adding antagonists such as the fungiTrichoderma and Gliocladium species. Such compost is called fortified compost.Management and control practicesPrevention activities :· Location: avoid placing the nursery in a densely shaded or humid place.· Disease chances will be reduced if fields are deeply plowed at least 30 days before planting toallow time for old crop and weed residues to decompose.· Remove crop debris as it may contain spores of damping-off fungi (and other pathogens).· Make sure the nursery is well drained and the soil is soft and crumbly.· Do not apply high doses of nitrogen. This may result in weaker seedlings which are more susceptibleto damping-off. Usually, when organic material has been incorporated in the soil before sowing,there is no need to apply additional fertilizer.· Add lots of compost or other decomposed organic material (15 to 20 tons/ha). Compost containsmicroorganisms and it feeds microorganisms already in the soil. An active population of microorganismsin the soil outcompetes pathogens and will often prevent disease.· Crop rotation: If you are raising cabbage seedlings every season, use fresh soil that has not beenused for cabbage or other cruciferous crops for at least 2 years. Plant another crop (not a cruciferouscrop) in the ‘old’ cabbage nursery.· Use vigorous seed or seedlings. Slowly emerging seedlings are the most susceptible.· Use seed that is coated with a fungicide layer. See section 3.3.· Soil sterilization is practiced in many countries, often as a preventive measure before sowing.There are many methods to sterilize small areas of soil. See details in section 3.7.1.· Consider using a layer of sub-soil (taken from a layer of soil below 30 cm) to prepare raisednursery beds. See section 3.7.1.3 for details.· Good results have been obtained with use of the antagonist Trichoderma sp. For example, applicationof Trichoderma harzianum is recommended by the Dept. of Agr. Extension in Thailand toprevent damping-off.· An interesting new option is the use of fortified compost. This is compost that contains theantagonistic fungus Trichoderma. Trichoderma is added to the compost after the primary heatingperiod of composting is complete. The Trichoderma fungus increases to high levels in the compostand when added to the soil, they are as effective as, or in many cases more effective, thanchemical fungicides for control of a number of soil-borne diseases, such as damping-off. Seesection 3.5.3.1 on composting.Cabbage Ecological Guide - 2000154

Major Diseases of CabbageOnce there is an infection in the nursery:· Unfortunately, the seedlings that are affected by damping-off cannot be saved anymore. To preventthe disease from destroying all plants in the nursery, you may consider uprooting the healthyseedlings if they are large enough to survive in the field. Chances of success, however, may not betoo great and many seedlings may still die. If the seedlings are still small, they cannot be transplanted.· Uproot and destroy diseased seedlings to avoid build-up of the pathogen population.· When the nursery soil is wet or waterlogged, dig a trench around the beds to help the water flowaway. It may slow disease spread to other parts of the nursery.· Good results have been obtained with use of the antagonist Trichoderma sp. For example, applicationof Trichoderma harzianum is recommended by the Dept. of Agr. Extension in Thailandmainly as a prevention but possibly as a control of damping-off. In Philippines, T. parceramosumand T. pseudokoningii are being tested. (FAO Dalat report, 1998).· If soil sterilization is not an option or is impractical, do not use the infected area for nurseries for atleast 2 seasons.· In some areas, fungicides are being used to control damping-off. Results vary however. In thisguide fungicide use is not recommended for control of damping-off.¤Points to remember about damping-off:1. Damping-off is a serious nursery problem, caused by several soil-borne pathogens.2. Damping-off occurs in areas with poor drainage or areas with a previous history of the disease.3. Crop rotation (including nursery site), proper drainage and sanitation practices (removing cropdebris) are ways to prevent disease problems.4. Good control of damping-off can be achieved by adding compost or other decomposed organicmaterial to the soil regularly.5. Additional prevention (mainly) and control can be obtained with use of the antagonistic fungiTrichoderma sp.8.2 Black rot - Xanthomonas campestrisSee plate 1 Fig. 3, 4 and 5Causal agent: bacterium – Xanthomonas campestrisWorldwide, black rot is considered to be one of the most important disease of crucifers.Signs and symptomsThe disease can affect both seedlings and mature plants. Leaves of affected seedlings turn yellow anddrop off prematurely. On older plants, V-shaped yellow lesions appear at the leaf margins with the pointof the V inwards. These lesions expand towards the center of the leaf. Affected areas turn brown and theplant tissue dies. The veins in affected areas are black in color. This can sometimes also be seen oncutting the stem of a leaf.Heads are dwarfed and lower leaves may fall off. Symptoms can be more severe on one side of the head.Soft rot often develops on affected heads as a secondary infection.Infection can occur in the seedbed, when seed leaves (cotyledons) and one or two lower leaves becomeinfected and drop off prematurely. With unfavorable conditions for further dissemination, the external signsof the disease may disappear for several weeks, but bacteria are still there, progressing slowly within thevascular tissue of the plant. Symptoms may appear in the upper leaves some weeks after transplanting.See section 7.7 on studying diseases in a “disease zoo”.155 Cabbage Ecological Guide - 2000

Major Diseases of CabbageSource and spreadThe black rot bacteria are carried over with infected seed and in the soil on diseased plant residues aslong as they are not decomposed. In addition, many cruciferous weeds can harbor the black rot bacteria.The bacteria can persist in residue for up to two years.When symptoms appear early in the season or even in the nursery, this may be a sign of the seed beinginfected with the bacterium. Infected seed will germinate and from their seed coats, the bacteria gainaccess to the cotyledon and into the young leaves. Leaf infection takes place through water pores(natural openings in the leaf) at the leaf margins, through stomata (another type of natural openings inleaves) and sometimes via wounds in the roots and leaves (for example due to insect feeding). Thebacteria further spread through the veins of the plant.Bacteria are spread by splashing or running water, wind-blown rain, by blowing of detached leaves,cultivating implements and infected seedlings. Insect transmission, for example by larvae of the cabbageworm, is known but not important. Overhead irrigation also spreads the bacteria, particularly in closeplantedconditions such as in the seedbed.Role of environmental factorsHot, wet conditions favor disease development. Under warm, humid conditions, symptoms appear 10 to14 days after infection. The optimum temperature for growth is 30-32 o C, maximum is 38-39 o C. Temperatureseems to be more critical than moisture.Importance - plant compensation - physiological impactThe damage to the yield and quality of the cabbage caused by black rot can be important when theinfection occurs early in the season (it then probably started in the nursery) and when the weather is hotand wet. Poor head formation and reduced yields are a result of the black rot infection. In the absence ofrain or overhead irrigation, which spread the disease, losses are much less. When infection occurs latein the season, usually no yield loss occurs.Once entered the plant, the bacteria travel through the veins of the plant. When a plant is infected, thebacteria can be present in the whole plant, even in the parts that show no symptoms. It is therefore noteffective to prune infected leaves to try to reduce the disease.Natural enemies/antagonistsUnknownManagement & control practicesPrevention activities :· Grow a resistant variety when you have had serious black rot problems before or know that blackrot is a problem in your area. Some varietal resistance has been reported but it is advisable to testdifferent varieties at local conditions.· At least three years’ rotation of the seedbed and the transplanted field with non-cruciferous cropsis advisable.· It is advisable to sterilize seed in water at 50 o C for 30 minutes before planting. That will kill bacteriathat stick to the seed. See section 3.3.Cabbage Ecological Guide - 2000156

Major Diseases of Cabbage· Practices such as dipping or spraying transplants with water after digging may spread black rotdisease and should be avoided.· Use other irrigation methods than overhead irrigation and/or irrigate in the morning when the leavesof the plants will dry quickly. The bacteria can easily spread with splashing water and soil particles.· Avoid planting downstream from infected fields. The bacteria may spread with the water runningdown from the infected field.· Control cruciferous weeds: they may be a source of infection.Once an infection is present in the field:· When symptoms of black rot appear in the nursery: do not transplant seedlings with symptoms.When many seedlings already show symptoms, it would be advisable not to use any of theseedlings because probably all of them (also the ones that look healthy now) will be infected.· When the plant is at the heading stage and only older leaves get infected, no action needs to betaken. The yield will not go down with a few black rot symptoms at old leaves. It is advisable notto grow crucifers for at least two years after harvest of this crop.· Sanitation: after harvest, remove all infected plants with roots from the field and either place themon a compost pile, feed them to cattle, or burn them. This will reduce bacteria surviving in the fieldon infected crop debris.· Biological soil sterilization or biofumigation could be options for testing. See sections 3.7.1.5 and3.7.1.6.¤Points to remember about black rot :1. Black rot is a bacterium that causes V-shaped yellow lesions at the leaf margins of older plants.2. Black rot survives on seed and residues of diseased plants and is spread mainly by water andon diseased seedlings.3. Use of resistant varieties where available, seed treatment, crop rotation, proper water managementand sanitation (removing infected plant material) are ways to prevent or reduce black rotinfection.8.3 Soft rot - Erwinia carotovoraSee plate 1 Fig. 6 and plate 2 Fig. 7Causal agent: bacterium – Erwinia carotovoraSigns and symptomsThe common name of this bacterial disease arises from the characteristic soft decay of the fleshy tissueof the plant. When soft rot affects a plant, the tissue softens, becomes watery and slimy. Cabbage plantsgive off an distinctive sulfurous odor. Affected heads decay rapidly and turn dark.157 Cabbage Ecological Guide - 2000

Major Diseases of CabbageSource and spreadThe bacteria survive in soil on decaying and dead plant debris. Wounds are the most common entry pointfor this bacterium. The infection can occur through surface areas like leaves injured by insects or mechanicalmeans or through damaged roots or stems. Bacteria spread through the veins to other plant parts.Some species of maggot fly are known to carry the soft rot bacteria. Eggs of the flies are laid in decayingcabbages and as the egg hatch, the larvae become contaminated with the soft rot bacteria. Infested adultflies lay eggs smeared with soft rot bacteria on maturing cabbage. The emerging larvae serve as vectorsas they feed on the cabbage and create wounds that allow the bacteria to infect the plant tissue.Role of environmental factorsWarm wet conditions promote disease development. Abundant moisture at the surface of the planttissue, where wounds are present, is essential for invasion. After infection has taken place, fairly highrelative humidity is needed for progress of the disease. When decaying cabbages are placed in a dryatmosphere, the rotted tissue dehydrates rapidly and further advance of the disease may be checkedcompletely.Soft rot can accompany mineral deficiency symptoms. Potassium deficiency or an unbalance of potassiumand other essential nutrients may bring about leaf scorching which may be followed by a bacterial attack.Soft rots are also common where an excess of farmyard manure is applied on poorly drained soils,probably due to the maggots attracted by the manure, as explained above.Importance - plant compensation - physiological impactSoft rot is mostly a problem shortly before the harvest period, when cabbage heads near maturation.Usually, the disease is very localized, only a few heads here and there drop out due to soft rot. In warm,wet conditions, the bacteria progress inside the plant and eventually, the whole cabbage head will berotten. Plant compensation does not take place at this stage. Often, farmers will quickly harvest headswith soft rot and peel off the outer affected leaves. The small remaining head may still be used forconsumption.Natural enemies/antagonistsUnknown.Management & control practicesPrevention activities :· Sanitation practices: make sure the field is clean from crop debris from a previous season. Also theborders of the field should be cleaned from crop debris.· Avoid injury to the crop - the wounds can be entry points for the bacteria.· Monitor field regularly and remove heavily infected heads from the field.· Crop rotation is probably of limited value for Erwinia because it can survive in the soil for many yearson dead plant tissue.Once an infection is present in the field:· Lightly infected heads can be harvested and the affected leaves peeled off. Those heads can still besold or used for home consumption.Cabbage Ecological Guide - 2000158

Major Diseases of Cabbage¤Points to remember about soft rot:1. Soft rot bacteria survive in soil on decaying and dead plant debris2. Wounds in plant tissue are entry points for soft rot bacteria.3. Avoiding crop injury and good sanitation practices (removing infected material) are ways toreduce spread of soft rot disease.8.4 Bottom rot – Rhizoctonia solaniSee plate 2 Fig. 8Other names: wirestem (seedlings) and head rot.Causal agent: fungus – Rhizoctonia solaniThis fungus is also a common cause of damping-off in seedbeds (see section 8.1 above). This sectiondescribes the disease as it occurs in the main field.Subspecies of Rhizoctonia solani can cause diseases in many crops: stem cancer and black scurf ofpotato, root rot of cotton and many others.Signs and symptomsBottom rot develops on plants after they have been transplanted to the field. Dark slightly sunken spotsdevelop on basal leaves near the soil. Affected plants are weak, produce small heads and sometimes wiltand die. In moist conditions and in storage, rot spreads to adjacent leaves and causes a head rot. Thewhole cabbage head may develop a dry rot, first restricted to the outer wrapping leaves. Tiny sclerotia(fungus reproductive structures) which are irregular and brown in color may form on the rot.Diseased plants appear in patches in the field, with the location and size depending on weather and soilconditions. If a field has symptoms of root rot, the plants that survive are probably also damaged and mayhave lower yield or show disease symptoms when stressed later in the season.Source and spreadThe fungus Rhizoctonia solan is a common inhabitant of field soils. It can survive on decaying and deadorganic matter in the soil.Bottom rot (and damping-off) occur in areas with poor drainage or areas with a previous history of thedisease.Role of environmental factorsDisease is promoted by moist conditions and high soil temperature. Root damage from salts and soilcompaction can also lead to increased loss due to root rots.Natural enemies/antagonistsUse of the beneficial fungus Trichoderma sp. has been reported to prevent or cure soil-borne diseasesincluding root rots. There are several species of Trichoderma. The species Trichoderma harzianum hasbeen used successfully in tropical climates but Trichoderma parceramosum also gave good results infield trials in Philippines (FAO-ICP progress report ’96 – ’99). In Thailand and Indonesia, for example,Trichoderma is available for use by farmers. There are more details on Trichoderma in section 7.10.1.There are several other antagonistic organisms, including bacteria (e.g. Bacillus subtilis, Pseudomonas159 Cabbage Ecological Guide - 2000

Major Diseases of Cabbagefluorescens) and fungi (e.g. Streptomyces griseoviridis, Trichoderma sp. and Gliocladium catenulatum)that control Rhizoctonia sp. These antagonistic organisms are available as biocontrol products registeredto control Rhyzoctonia and related soil-borne disease in the United States. Some of these products maybecome availabe in Asia in the future. (www25; www29)Management & control practicesSee section 8.1, damping-off. The same practices apply for bottom rot.¤Points to remember about bottom rot :1. Bottom rot is caused by a soil-borne pathogen that survives on decaying and dead organicmatter in the soil. The same fungus also causes damping-off in seedlings.2. Bottom rot occurs in areas with poor drainage or areas with a previous history of the disease.3. Optimizing drainage and growing conditions, using vigorous seed and transplants, crop rotation,and sanitation practices (removing crop debris) are ways to prevent disease problems.4. Good control of bottom rot can be achieved with use of the antagonistic fungi Trichoderma sp.There are many other effective biocontrol products which may become available in Asia in thefuture.8.5 Leaf spotCausal agent: several fungiLeaf spots on cabbage can be caused by several fungi. Each fungus can cause slightly different symptomsand the pathogen can sometimes only be distinguished with a microscope, which is usually not availablein the field. The most common leaf spot fungus is Alternaria brassicae, which is described below. Otherfungi causing leaf spot on cabbage include Mycosphaerella brassicicola, Phoma lingam (see section8.8) and Cercospora sp.In the field, the difference between the various fungal leaf spots is not always easy to make, especiallywith early symptoms. Note that for a proper decision on the management of fungal leaf spot, it is notalways necessary to be able to distinguish the different causal organisms. Most fungal leaf spots willneed the same management practice, mainly reduction of the source of infection by sanitation.Alternaria leaf spot - Alternaria brassicaeSee plate 2 Fig. 9This fungal disease is also known as black mold, gray leaf mold or blackspot.Causal agent: fungus – Alternaria brassicaeSigns and symptomsSymptoms of Alternaria leaf spot usually appear on the older leaves of the cabbage plant. The spotsbegin as black pinpoint-size spots and enlarge to distinct, brown-black leaf spots of 1 to 2 cm diameterwith concentric rings and sometimes a yellow area around the spot. The concentric rings contain theCabbage Ecological Guide - 2000160

Major Diseases of Cabbagespores with which the fungus spreads. These have a dark, dustyappearance. Spores develop on the leaf spots during moist periods.The fungus occasionally attacks seedlings in the nursery. Thesymptoms occur immediately after germination as dark spots onthe seedling stem, which causes damping-off or a stunting of theyoung plant. Alternaria leafspot also infects Brussels sprouts andcauses brown rot of cauliflower.Source and spreadAlternaria sporesAlternaria leaf spot can be transmitted on the seed and in plant debris. It also survives on cruciferousweeds. Infected crop residues are a major source of infection for the next crop, or a neighboring field.Even old leaves that are completely dead and dried, can still contain living spores of the fungus! Singlespores cannot survive in the soil, except when they are on a lesion on a piece of old leaf. Alternariaspores are easily spread by wind, splashing rain, machinery or farm tools and workers when the plantsare wet.Role of environmental factorsCool, wet weather favors disease development. This is why leafspot is usually not a problem during thedry season, but it can be severe in the wet season.Rain and humid weather are favorable for spore development. Infection may occur when leaves are wet formore than 9 hours. This can also be caused by use of overhead irrigation or sprinklers, especially whenused in the late afternoon. This results in wet leaves which will not dry up quickly. Overhead irrigation canbest be used in the morning when the sun will dry the leaves of the plant. Even better is to use furrowirrigation.In seedbeds, Alternaria leaf spot can be stimulated by high humidity due to overwatering, dense seedingand heavy dew.Importance - plant compensation - physiological impactLeaf spots reduce the area of leaf producing nutrients for the plant (photosynthesis). As the leaf spotfungus usually attacks the older leaves, in which the photosynthetic activity has gone down anyway, theeffect on yield and quality of the cabbages will not be severe. When the leaf spot infection is not seriousand only affects the older, dying leaves of mature cabbage plants, no control is necessary.When the infestation of leaf spot is severe, e.g. when seedlings are already affected or when leaf spotsare also found on the cabbage heads, control measures may be considered because yield and quality ofthe cabbages can be reduced.Leaf pruning to control leafspot…During a Training of Trainers (TOT) in the Philippines, a study was done with hand-picking of oldinfected leaves. The idea was that removing leaves with lesions would reduce the severity and spreadof the disease. The disease severity and yield of the pruned field were compared with the unprunedfield. Results varied from no effect (same disease incidence and same yield but labor costs forpruning higher) to a negative effect (lower yield in the pruned fields) (pers. comm. cabbage TOTparticipants Cordilleras, 1994/95). LIt may still be a good idea to test during the wet season, when disease incidence is high. J161 Cabbage Ecological Guide - 2000

Major Diseases of CabbageNatural enemies/antagonistsThere are fungi, such as Aureobasidium pullulans and Epicoccum nigrum, that have an antagonisticeffect on Alternaria sp. To date however, none of these have developed into a product that can be appliedas a control measure against leaf spot.Management & control practicesPreventive activities :· Use a crop rotation plan: do not grow any type of cruciferous crop for at least 2 years.· Use clean seed that is coated with a fungicide or treated in hot water of 50 o C for 30 minutes. This willkill spores that are attached to the seed. See section 3.3.· Practice sanitary measures such as the use of clean seed beds away from other crucifer productionand the destruction of cruciferous weeds. Plant seedlings in a field where crop debris is removed,even from the borders of the field. Even dead cabbage leaves may still contain living spores of thedisease!· Plant resistant or tolerant varieties where available to reduce disease incidence.· Use a planting site and plant spacing pattern that expose plants to full sun throughout the day.· When planting, orient rows in the direction of prevailing winds for better circulation of air through thefoliage.· Avoid over-planting or crowding plants as this increases the drying time.· In order to reduce disease spread by hand or machinery, avoid working in fields while the plants arewet.Fungicides for leafspot control, a study example from Vietnam:In Dalat, in the central highlands of Vietnam, a study was done (Feb-May 1995) to compare the effectof fungicide aplications on yields and disease level. Fungicides were applied twice per week andcontrol plot received no fungicides. It was found that disease levels did not differ in the sprayed andunsprayed plots and cabbage yields were the same. Economic benefits in the fungicide treatmentwere VND 1.6 million/ha lower! L(FAO Updates on Vietnam National IPM programme in vegetables, 1999)Once the disease is present in the field:· When only older leaves are affected, no control is necessary. After harvest however, it IS necessaryto remove old leaves. These leaves should be taken off the field and either fed to cattle, buried in a pitor put on a compost pile away from the field.· Some fungicides are effective in stopping spread of this fungus. Be careful for the effect of fungicideson the natural enemy population of insect pests! See box in section 4.9.· Plowing immediately after harvest helps eliminate the sources of airborne Alternaria and encouragesthe rapid decomposition of crop residues.Cabbage Ecological Guide - 2000162

Major Diseases of Cabbage¤Points to remember about Alternaria leaf spot:1. Alternaria is a wet season problem.2. Alternaria leaf spot is introduced on infected seed or by wind-blown spores from nearby cruciferweeds or old crop residues.3. Leaf spot usually occurs on older leaves only and chemical control is therefore not necessary.4. Sanitation (removing crop debris and taking it (far!) away from the field) is the key to leaf spotmanagement.5. Any practice which promotes the rapid drying of leaves and soil will help reduce leaf spot disease.8.6 Clubroot - Plasmodiophora brassicaeSee plate 2 Fig. 10 and 11Causal agent: fungus – Plasmodiophora brassicaeSigns and symptomsClubroot causes wilting and yellowing of the above-ground parts. Oftenmature plants wilt during hot days but may recover during the nights.Plants stay smaller in size and often develop no heads. The best diagnosticsymptom is the presence of big spindle-shaped enlargements (the “clubs”)on the roots. This may occur on fine roots, secondary roots and the maintaproot. Sometimes, the fungus can enter through wounds in the stem atsoil level - the clubs then appear there and just below soil level. The lowestleaves of the plant may turn yellow and drop off.The fungus can attack both seedlings and mature plants. Symptoms ofseedlings may only be detected when the plants are pulled.The disease is often most severe in low-lying, poorly drained soils.Secondary invasion by other pathogens like soft rot bacteria may occur.Source and spreadThe fungus is soil-borne and enters the plant through fine hair roots or through wounds in secondary rootsor in the stem. The disease is spread by soil particles (soil easily clings to shoes or slippers and to toolsused in the field), by transplants and by drainage water. Clubroot is not seed-borne. Transplants areusually the main means of widespread distribution.Every infected plant with clubs is a little timebombM. The clubs are full of fungus spores. These sporesare released into the soil when the root decomposes. That happens when infected plants are not removedfrom the field. The spores of clubroot are very persistent and can stay alive in the soil for many years(from 7 to 20 years!). This is because the spores have a very thick skin that protects them from drying outand from high temperatures.163 Cabbage Ecological Guide - 2000

Major Diseases of CabbageþHow to test your soil for presence of clubroot:The easiest way is to uproot several cabbage roots at harvest and check them for clubs. If you findsome roots with clubs, the soil is infected.When you do not have that possibility, another option to check the soil for presence of clubroot is thefollowing trial. This trial is however more time consuming (takes at least one month) and there is arisk that you will find a “false negative”: the soil is infected but you don’t find it in the trial.Take some soil from different portions of the field. Put it in pots and sow some cabbage seed (canalso be Chinese cabbage as this is very sensitive to clubroot) per pot. Keep the soil in the pots moistand look after the emerging seedlings for about 3 - 4 weeks. Seedlings with at least 3 true leaves canbe uprooted, and washed to remove the sand from the roots. Carefully check the roots for smallclubs. If you find clubs, the soil is infected.Since clubroot can be very localized in a field, the more soil samples and pots you take for this test,the better your conclusion will be. That reduces the risk of missing an infection.Role of environmental factorsThe temperature range in which the fungus is active is 9 - 35 o C with an optimum temperature for fungaldevelopment of 24 o C. Infection is limited by low soil moisture. A common observation is that the diseaseis most severe in low-lying, poorly drained soils.A soil pH of less than 7 favors disease development. When the pH is 7 or higher, the spores of the fungusgerminate poorly or not at all.W here potatoes are grown in rotation with cabbage:While clubroot of crucifers is suppressed by a soil pH above 7, potato scab (Rhizoctonia solani) isknown to be stimulated when the soil pH raises. This is particularly true in sandy soils, less in claysoils. A pH below 5.2 will reduce soil-borne scab in potato. That means that when soil pH is raisedwith lime to levels above 5.2, chances are that a following potato crop may develop symptoms ofscab. In general, potatoes prefer a more acidic soil than cabbages. It depends on factors like severityof the diseases, economics, etc. what crop should have the priority of soil pH adjustment.Importance - physiological impact - plant compensationGiven the fact that once the soil is infected with clubroot, the disease can stay in the soil for more than7 years, even if no cabbages or other cruciferous crops are grown, the fungus is one of the most persistentdiseases known in vegetable growing. In an infected field however, only seldom all plants are affected.Mostly the disease is localized, with groups of plants dropping out. Therefore, in an infected field, it is stillpossible to grow cabbage. The key is to keep the fungus from multiplying too much. See under preventionactivities below. Severely infected fields however, become unfit for cabbage (and other crucifer) cultivation.Once the fungus enters the fine roots of a cabbage plant, the plant reacts by making the clubs, cancerlikeenlargements in the roots. Water and nutrient uptake are severely restricted by this and the plantcannot develop normally but it will not die immediately because there are still some roots left for waterand nutrient uptake. In the middle of a warm, sunny day however, the plant may wilt.Usually, symptoms are localized near the point of infection. The fungus does not move through the plantveins. When only a small part of the root system is infected with clubroot, a head can still be formed.New roots are generated that will compensate for the loss of part of the roots. Often, these plants and theheads will be small in size but still look relatively healthy. When a plant is suspected of having clubrootCabbage Ecological Guide - 2000164

Major Diseases of Cabbagebut does not look severely infected, it is possible to leave it in the field until the harvest. During harvesttime, uproot the whole plant and if the roots of the plant are affected, take those plant parts aside fordrying and burning afterwards. Don’t leave infected plants in the field. Severely infected plants will notform a head and should be removed from the field. See section below on management and control.Natural enemies/antagonistsBiological control of clubroot with Trichoderma sp. may become an option in the future. In studies withChinese cabbage in New Zealand for example, seventeen of the 25 isolates of Trichoderma sp. reducedclubroot severity compared to the untreated control. Field trial results with two Trichoderma isolates,applied as a root dip before transplanting, gave reduction of club weight on roots but did not increase thetop weights of the plant. L(Cheah et al, 1996, www28).Management & control practicesPrevention activities:· Resistant varieties: some differences in susceptibility between varieties has been reported but it isadvisable to test varieties at local conditions, for example in varietal trials.· Select clubroot-free nursery soil that is well drained. The preferred nursery has not grown crucifersfor many years.· Because clubroot is so long-lived, crop rotation is probably not effective. Fields once severely infectedwith the clubroot pathogen remain so indefinitely and become unfit for cultivation of brassicas.· Raising soil pH to a neutral level of around pH 7 by broadcasting and incorporating hydrated lime intothe soil offers some control/protection. This liming should not be done more than once every 3 yearsto keep the soil from becoming too alkaline, nor is it very effective on light, sandy soils. Guidelines toraise the pH are given in section 3.4.6.· Use healthy seedlings. Do not transplant seedlings that have little clubs or swollen roots that do notlook normal. In fact, no plants from a seedbed that has even a single clubroot seedling in it, shouldbe transplanted into a disease-free field! if any transplants have clubroot symptoms, many others arecertain to be infected, even though symptoms may not yet have appeared!· Remove weeds, there are many cruciferous weeds that can be a host of clubroot and other cabbagediseases.· Be careful with fields of other farmers that do have a clubroot infection. If you visit an infected field,make sure there is no soil attached to your slippers, shoes or farm tools when you return to your ownfield. You can easily transport the disease with the soil particles!It was noted that some farmers, who had serious clubroot problemsin their field, could easily recognize clubroot infected plantsby the small plant size. But instead of roguing the plants, theyapplied foliar fertilizer to these small plants in an attempt to get atleast a little head from these small plants. However, comparing thecosts of a foliar fertilizer (quite expensive!) to the additional income of a few small,low quality heads AND the risk of giving the pathogen a chance to multiply, and spread into otherparts of the field, make this practice not very attractive.Remove infected plants: they will not give you much yield (and income) and infected plants in thefield will lead to MORE disease!165 Cabbage Ecological Guide - 2000

Major Diseases of CabbageOnce there is an infection in the field:vuproot infected plants including all roots and destroy them but.....:· do not throw the infected plants at the side of the field. From there, the spores will be releasedinto the soil and may spread into the field again. The result: you have helped spread the disease!· do not put uprooted clubroot plants on a compost pile. When the temperature inside the compostpile is not high enough (above 60 o C), the spores will not be killed and may be spread intothe field again with the compost. Temperatures above 60 o C should kill the spores inside acompost pile, but it is difficult to tell whether the temperature inside the pile reached that level fora sufficient period of time.· uprooted clubroot plants should not be fed to farm animals as the spores are so strong that theycan survive passing through stomach and intestines. As a consequence, spores will be spreadwith the manure of the animals.· leave infected plants to dry for some time and burn them. It’s the safest way to be sure to haveremoved the spores.· unfortunately, by uprooting a diseased plant, the disease is not removed from the soil. Thefungus is still present in the soil area around that infected plant. By removing the infected plant,you have only accomplished that the disease will not spread further.vvvvvCheck the pH, if it’s too low, apply lime to raise it. Applying wood ashes also helps to raise pH. Theinfection will be less with a pH of around 7.When the soil is very heavily infected with clubroot, consider growing another crop. Even after applyinglime, it may still take several seasons before the pH has risen enough to suppress clubroot.Soil sterilization: several trials were done, for example in the mountain areas of the Philippines, totest if solarization would control clubroot. High soil temperatures (over 60 o C), due to heating up of thesoil under the plastic sheets should kill spores of the fungus. The results of the trials varied considerably,therefore, no recommendation for use of this technique is given in this guide. It may however,be interesting to try in a small area of an infected field, but preferably combined with liming the soil.See section 3.7.1.2 and 3.4.6.Applying fungicides is not effective to control this fungus. This is first of all because the spores arevery strong and may still be inside the plant roots. Secondly, the fungus can be located deep in thesoil and where pesticides may not reach.Chitosan, a naturally derived component (polysaccharide) from the outer skeletons of crab, mayhave potential for clubroot control. Chitosan has been shown to be effective for control of Sclerotiniarot (caused by Sclerotinia sclerotiorum) of carrots (Cheah et al. 1997). In studies with Chinesecabbage in New Zealand, it significantly reduced the club weights.¤Points to remember about clubroot :1. Clubroot is a fungal disease that causes enlargements (the “clubs”) on the roots, resulting inwilting of the plant during warm days and small head sizes or none at all.2. Clubroot is spread by soil particles, by transplants and by drainage water. Transplants areusually the main means of widespread distribution.3. Resistant varieties, use of clean transplants, removing weeds, raising soil pH to7 or above, andproper sanitation practices are ways to prevent or reduce clubroot infection. Soils (severely)infected become unfit for cultivation of crucifers. Trichoderma may become a biocontrol option inthe future.Cabbage Ecological Guide - 2000166

Major Diseases of Cabbage8.7 Downy mildew - Peronospora parasiticaSee plate 2 Fig. 12 and plate 3 Fig. 13Causal agent: fungus – Peronospora parasiticaThis disease can be particularly damaging during the nursery stage or in a newly transplanted crop.Signs and symptomsSmall yellow spots develop on the leaves and cotyledons of young plants in the seedbed. The spots laterturn brown. In moist weather, a white downy mold develops on the underside of the spots. The mold arethe spores structures of the fungus. The spores can sometimes stick to your finger as a white powderwhen you wipe the underside of the leaf. Dead leaf areas appear in the yellow zone on top of the leaves,which often have a speckled appearance. The young leaf or cotyledon, when yellow, may drop off.Symptoms of the disease on mature plants are yellowish-brown areas between the main veins. Again,during moist weather, white downy patches of the fungus can be seen on the underside of the leaves.Severely infected leaves do not drop off and infected areas gradually enlarge, turn bright yellow, thenbecome tan and papery. Occasionally, affected leaves will show hundreds of very small, darkened specks.On cabbage heads, the pathogen may cause numerous sunken black spots, varying in size from tinydots to larger areas. Sometimes, a downy mildew infection can predispose plants to bacterial soft rot.Source and spreadThe fungus spreads with seed, and can stay over in roots and in decaying portions of diseased plantsand on cruciferous weeds. In areas with a cold winter period, thick-walled resting spores may form instems, cotyledons, and other parts of infected plants. On growing plants, the fungus produces largenumbers of spores that are blown about by wind and splashed by rain.Spores carried by wind can float long distances.When the fungus is attached to seed, it is carried aboveground on new shoots. The mycelium (threads ofthe fungus) can penetrate leaves through stomata (natural openings in the leaves) and grows inside theplant tissue. The spore-carriers grow to the surface again, mostly on the underside of the leaf, to releasethe spores. If weather is favorable, spores germinate in only three to four hours, and infect new planttissue and produce new spores in three to four days.Role of environmental factorsCool nights with moderate daytime temperatures (optimum temperature is 15 - 18 o C) associated withhigh humidity are conditions that promote disease development. High humidity is likely to occur duringthe rainy season, during periods of heavy dew, when overhead irrigation is used and when plant densityis close. Presence of a water film on the foliage from fog, drizzling rain, or dew allows spores to germinate,infect, and produce more spores on a susceptible host in as few as 4 days.Importance - plant compensation - physiological impactThis disease is most serious on young seedlings; if cotyledons and the first true leaves are severelyinfected, the young plant may die. Damage to mature plants in the field is usually of minor importance.In Chinese cabbage, downy mildew may also cause severe losses in mature crops.Natural enemies/antagonistsUnknown.167 Cabbage Ecological Guide - 2000

Major Diseases of CabbageþStudy of spread of downy mildew:Take a number of leaves with white downy mold on the underside. Put these leaves in a smallquantity of water and stir firmly. Remove the leaves from the water. The spores on the white mold willbe released into the water. The water has now become a source of infection. Take a few pots containinga bundle of cabbage seedlings each and sprinkle the water over the plants. Treat a similar pot withseedlings with clean (uncontaminated) water as a control. Cover the pots with a plastic bag to keepa high humidity inside. Keep plants at a cool place for a few days. Depending on temperature andhumidity, symptoms will appear on the leaves.Management & control practicesPreventive activities:· Use a crop rotation plan: do not grow any type of cruciferous crop for at least 2 years.· Use a resistant/tolerant variety. Disease resistant varieties are not available for most cruciferouscrops. However, differences in varietal susceptibility have been reported. Some hybrid varieties ofbroccoli are resistant or tolerant to downy mildew. It is advisable to test varieties under localconditions. See section 3.2.2.· Use clean seed that has been hot-water treated and/or coated. See section 3.3.· Practice sanitary measures such as the use of clean seed beds away from other crucifer productionand the destruction of plant debris and cruciferous weeds.· Use a planting site and plant spacing pattern that expose plants to full sun throughout the day.· When planting, orient rows in the direction of prevailing winds for better circulation of air throughthe foliage.· Thin out seedlings to about 2-3 cm apart. Closely planted seedlings will result in a high humidityand may stimulate infection.· In order to reduce disease spread by hand or machinery, avoid working in fields while the plantsare wet.Once the disease is present in the field:· When seedlings show symptoms of downy mildew, try applying some extra nitrogen. Seedlingstend to outgrow the disease if they are top dressed with a nitrogenous fertilizer.· If severe disease pressure is expected, timely application of a registered fungicide before theonset or at the very beginning of the disease may reduce the severity of the disease. This isusually only necessary to protect young seedlings. Repeated applications may be required, dependingon weather. Consult local extension agencies for current fungicide recommendations.· When symptoms appear on mature plants at a late growth stage, usually no control is necessary.· Plowing immediately after harvest helps eliminate the sources of airborne downy mildew sporesand encourages the rapid decomposition of crop residues.¤Points to remember about downy mildew:1. Downy mildew is destructive only in seedbeds and on young transplants during cool, rainy weather.2. The pathogen survives between seasons in crucifer weeds, seed and crop residues. Spores arespread to new crops primarily by wind and splashing rain.3. Any practice which promotes the rapid drying of foliage and soils will help minimize diseaseincidence.Cabbage Ecological Guide - 2000168

Major Diseases of Cabbage8.8 Black leg - Phoma lingamSee plate 3 Fig 14Causal agent: fungus – Phoma lingamAnother fungal pathogen causing similar symptoms is Leptosphaeria maculens.Signs and symptomsSymptoms begin as dark sunken spots at the base of the stem and may appear later on the leaves aslight brown circular leafspots. Infected plants remain smaller in size. Stem spots enlarge and girdle thestems, mostly at the soil level, causing the plant to suddenly wilt and fall over. The stem can feel dry andwoody and the tissue has turned black, sometimes with a purplish margin.In an advanced stage of black leg, the leafspots carry distinct black dots on the diseased areas of theplant. These are fungus spore-carrying structures (pycnidia).The disease can infect both seedlings and mature plants. The fungus can infect plants during germinationof the seed. The first signs of the disease then occur on the seed leaves (cotyledons). The resultingfalling over of the seedlings is difficult to distinguish from damping-off disease caused by other fungi. Thefungus produces many spores on prematurely killed seedlings and these are able to cause many secondaryinfections in the seedbed.The root system is gradually destroyed, although plants may survive in damp soil when new rootsdevelop above diseased parts. Infected plants will eventually die. Weather conditions determine how fastthe plants will fall over.Source and spreadThe fungus can persist on seed and in residue from diseased plants. It can persist in residue for about 3years. If infected plants are not removed from the field, the fungus can easily spread to neighboringplants. The fungus can be carried on seed and on transplants. Spread in the field can be due to splashingand running contaminated water or by workers and implements that move through fields that includediseased plants. Wind can carry spores over long distances.Wounds can facilitate the fungus entering into the plant. A few infected seedlings from the nursery caneasily infect many other seedlings through small wounds in leaves and roots due to uprooting.Role of environmental factorsThe growth speed of the fungus in the plant depends on the temperature. Below 10 o C and above 28 o C, thefungus is not very active. The optimum temperature for Phoma lingam is around 15 o C.The fungus needs a high humidity for the release of the spores from the pycnidia, the spore-carryingstructures. The spread of the spores is dependent on rain: splashing rain (or irrigation!) drops can carrythe spores to other plants. High humidity or rain is also needed for the spores to germinate on cabbageplants.Wind can carry spores quite long distances.Natural enemies/antagonistsUnknown.169 Cabbage Ecological Guide - 2000

Major Diseases of CabbageManagement & control practicesPreventive activities:Most preventive activities as described for clubroot and black rot also apply for black leg disease (exceptfor the pH factors for clubroot). In summary:· Crop rotation: rotate both cabbage nursery and production field by not growing cruciferous cropsfor at least 3 years.· Use of clean seed: either certified by a reliable seed company, or treated seed. See section 3.3.· Use of clean transplants: Seedlings should not be transplanted from seedbeds that show anydiseased plants.· Avoid overhead irrigation. The splashing water may spread the disease.· Ensure good air circulation, drainage and rapid evaporation of dew, e.g. by wide spacing, orientingrows in the prevailing wind direction, choosing a sunny planting site, etc.· Sanitation: clean the field of old leaves and other crop left-overs before transplanting seedlings.· Diseased leaves should not be fed to farm animals if manure is to be used on crucifer fields:researchers report that manure from cattle fed on black leg debris is an important infection source!Once the disease is present in the field:· Remove infected plant material. Take it away from the field to a compost pile, or a place far fromthe production field.¤Points to remember about black leg:1. Black leg can cause “damping-off” type symptoms in seedlings and leaf spots in older plants.2. The fungus can survive on seed and in residue from diseased plants. Splashing water, fieldworkers, and wind can spread the disease.3. Sanitation (removing and destroying) infected plant material) is the main management practice.8.9 Physiological disordersPhysiological disorders are “diseases” caused by adverse environmental conditions. Major causes ofthese disorders are excessively high or low temperatures, soil-moisture disturbances, sun burn, pesticideburn (when the leaves of a plant turn brown-black when the dose of a pesticide is too high), nutritionaldisorders, and even air pollution.Fertilizer deficiencies (sometimes due to too low a soil pH) are a common cause of physiological disorders.If a plant is not supplied with sufficient amounts of the fertilizer elements it needs for good growthit will develop symptoms of lack of nourishment. These symptoms are specific for a crop and for afertilizer element. Deficiencies may often develop on light sandy soils that let rain water through easilyand allow nutrients to leach away. On the other hand, over-fertilization may also cause severe growthdistortions in plants.Some of the most common physiological disorders for cabbage are listed below. See also section 3.5.7.on fertilization needs of cabbage and box on deficiency symptoms for macro and micro nutrients insection 7.6Cabbage Ecological Guide - 2000170

Major Diseases of CabbageNitrogen (N) deficiencyIn cabbage plants, symptoms are usually a purple glow on the leaves. Symptoms are located throughoutthe plant, although the older leaves usually show symptoms most clearly. When nitrogen deficiencyoccurs early in the growing season, the plants may stay small in size and head formation may bedistorted. In light, sandy soils, nitrogen deficiency can easily occur after heavy rainfall. The rain will washthe nitrogen out to deeper layer of the soil where it is inaccessible for the crop.Adding nitrogen (chemical fertilizer) is usually sufficient to overcome nitrogen deficiency for the shortterm. Adding organic material to the soil improves nutrient holding capacity of the soil and it therefore amore permanent solution.Nitrogen (N) excessToo much nitrogen leads to tall, weak plants. Plants basically grow “too fast” and become weak andtherefore more susceptible to diseases. Sometimes, no cabbage heads develop. In addition, too muchnitrogen may result in a high concentration of nitrate in the leaves which is detrimental for humanhealth L.Phosphorous (P) deficiencySymptoms of phosphorous deficiency are plants that stay small in size. Leaves are dark green to bluishgreen in color. Sometimes, a purple color at the undersides of the leaves can be seen. Symptoms arelocated throughout the plant. It is difficult to correct deficiency symptoms with additional fertilizer applicationonce the symptoms are there. Proper fertilization before the crop is transplanted and use of lots of (welldecomposed)organic material is the best prevention.Potassium (K) deficiencySymptoms of potassium deficiency are a bluish-green coloration followed by yellowing and scorching ofthe leaf margins, accompanied by poor heading. The symptoms are located mainly at the older leaves.Potassium deficiency symptoms are liable to occur on land recently broken up from grass, on light soils,on heavy soil with deficient drainage and in land heavily manured with nitrogenous materials.Boron deficiencyCabbage heads may be small and yellow. The stems of cabbage may be cracked and corky. Leaves maybecome dry and papery. Light soils are more susceptible to boron deficiency, especially in very dryperiods. Also, soils with high pH are more susceptible to boron deficiency.Boron can be added to soils separately but a soil test is advisable to ensure that boron levels are not toohigh.Magnesium (Mg) deficiencyThe symptoms of magnesium deficiency are pale marbled areas between the veins (chlorosis), sometimesaccompanied by a purple color of the leaves. The pale areas finally dry out into brown dead patches. Thesymptoms are located mainly at the older leaves.Growth and maturity may be greatly checked and the plants may become badly affected with diseaseslike downy mildew.171 Cabbage Ecological Guide - 2000

Major Diseases of CabbageDeficiency of magnesium may occur both on acid soils and on soils containing ample supplies of lime,especially where this has been added. It is most prevalent on light soils under conditions where themagnesium is readily leached away, like in wet seasons. The deficiency may become apparent afterseveral years of routine manuring with inorganic fertilizers.In acid soils, magnesium limestone may be applied to counteract the deficiency. Other magnesiumcontaining fertilizers like magnesium sulfate can also be used, preferably before the seedlings aretransplanted. The turning-in of green manures and the use of farmyard manure or compost also tend topreserve supplies of magnesium in the soil.List of related disease exercises from CABI Bioscience/FAO manual:3-A.1. Study of symptom development of leaf spots: classroom exercise3-A.2. Study of symptom development of leaf spots: field exercise3-A.3. Effect of infection of the seed bed3-A.4. Effect of the use of infected planting material3-A.5. Test effect of hot water seed treatment3.B.1. Seed drenching/coating to manage damping-off3-A.6., 3.B.2 and. 3.D.2. Use of subsoil to manage diseases in the nursery3-A.7., 3. B.3. and 3.D.4. Soil solarisation to manage diseases in the nursery3-A.8., 3. B.4. and 3.D.3. Steam sterilisation to manage diseases in the nursery3-D.5. Test effect of soil solarisation in the field3-A.9. Test effect of infected crop debris in the field3-E.4. Sanitation measures to manage cabbage soft rot3-A.10. and 3-E.2. Effect of rain on the spread of diseases3-A.11. and 3.E.1. Spread of diseases by farming tools3-A.12. and 3-E.5. Test different cultivars for resistance to diseases3-A.13. Pruning and plant compensation3-E.3. Pruning of infected shoots versus fungicide application3-A.14. Restricted fungicide use to manage leaf spots3-A.16. Study of spread of a fungal leaf spot3-D.1. Pot experiments to test whether root diseases are soil-borne3-D.6. Effect of liming on clubroot of cabbage3-F.9. Virus or nutrient deficiency?Cabbage Ecological Guide - 2000172

Weed Management9WEEDMANAGEMENTSUMMARYA good weed IPM program is one that will manage existing weeds economicallyand prevent a buildup of weed seed or tubers, rhizomes, etc. in the soil.The most important time to keep the field free of weeds for cabbage production isgenerally in the first 3 to 4 weeks. By then, the crop is large enough to shade outlate-emerging weed seedlings or is otherwise competitive with weeds.Before and after this weed-free period, weeds can be suppressed by severalcultural practices including mulching, and cover crops. Weed prevention practicesare listed in section 9.4. Dependence upon herbicides alone does seldom providethe most economical weed control. Good cultural and crop management practices,are the backbone of any weed management program. Biological weed controloptions, such as weed-controlling fungi, are being studied and may becomeavailable in the near future.173 Cabbage Ecological Guide - 2000

Weed Management9.1 Weeds: good or bad?LWeeds in a cabbage field are usually unwanted because they compete with cabbage plants forwater, nutrients, and sunlight. They may harbor insect pests and diseases or form breeding places forpest insects. In addition, the presence of weeds decreases air circulation between the plants, increasingthe humidity inside the crop. This can lead to more diseases, because many (fungal) diseases needhumidity to infect a plant. Weeds may also directly reduce profits by hindering harvest operations,lowering crop quality, and produce seed or rootstocks which infest the field and affect future crops.Weeds are normal plants, but they are “weeds” because they grow where wedo not want them.J But there can be some good points of weeds too: many weeds makegood compost, several are edible for human use or when fed to farmanimals. Weeds have consumed nutrients from the soil and these can bereturned to the soil by using weeds as mulch or as “green manure” (seesection 3.5.3.2).There are also weeds that have a medicinal use. Under certaincircumstances, weeds may have a beneficial effect in preventing soilerosion. And, very important, some flowering weeds can be food sourcesfor adult parasitoid wasps that feed on the nectar inside the flowers, andprovide shelter places for predators and other beneficial insects.Weeds can be indicators of soil fertility. Chan (Imperata cylindrica) forexample is a very common weed in Bangladesh, growing only where soilis very infertile. This gives valuable information on the status of the soil.Imperata cylindrica9.2 Types of weedWeeds can be classified in several ways. The most commonly used classifications are:Annual or Perennial1. Annual weeds: these are the most common weeds that germinate,flower, produce seed and die within one year. In some casesannual weeds have several generations per year. Most areproducing a lot of seed. The seed can remain viable for manyyears in the cool depths of the soil, ready to germinate whenexposed by cultivation to light and moisture.2. Perennial weeds: those weeds that remain in the soil from oneyear to the next. They often require more than 1 year to completetheir life cycle. Typical perennial weeds have deep roots or creepingrunners which spread vigorously, or roots which can resprout fromsmall fragments left in the soil.perennial weedCabbage Ecological Guide - 2000174

Weed ManagementBroadleaf weeds or grasses1. Broadleaf weeds: germinating seedlings have two leaves. Theleaves are usually wider than those of grasses. Broadleaf weeds arebasically all weeds except grasses, sedges and bamboo.2. Grasses: seedlings have only one leaf. Next to grasses, other commonweeds in this group are sedges and bamboo.The SeedbankTo check if there are weeds in your soil, this exercise is a useful one. Take a portion of soil from thefield (about half a bag full) and bring it to the ‘classroom’ or any other place near the house. Put thesoil on a piece of plastic. Water it and leave it for several days. Keep the soil moist but do not makemud out of it! Seeds of weed will germinate in the next days and you can check how many weedscome up and which species of weed they are.soilpiece of plastic9.3 Control or management?Similar to disease and insect management, weeds also must be managed. Weed management meansa range of activities that support each other. Some of these activities should be done during crop growth,some even before sowing the seeds. Weed management, just like insect and disease management, isa long-term activity, sometimes it is a planning for several years. Control is a short-term activity, focusedon killing or removing weeds from the field.A good weed management program is one that will control existing weeds economically and prevent abuildup of weed seed or tubers, rhizomes, etc. in the soil. Integrated pest management of weeds, likeinsect and disease IPM, focuses on prevention, beginning with identification of weed species. Such aprogram includes integrated use of several crop management practices which may include any of preventionpractices listed in section 9.4 below.Is 100% control of all weeds necessary?The ultimate goal of growing vegetables is to maximize profits. While it is true that crops are able totolerate a certain number of weeds without suffering a yield reduction, it is first important to consider175 Cabbage Ecological Guide - 2000

Weed Managementweed problems on an individual basis. There are some weeds for which 100% control may be desirablebecause they are particularly competitive, persistent, or difficult to control. Identification of weed speciesis therefore a first step in weed management.Weed management should also be related to growth stage. It may be necessary to go for 100% weedcontrol in the first few weeks after transplanting but when plants are fully grown, some weeds may betolerated. Such weed-free period is called the critical weed-free period, a concept explained below.Critical weed - free periodThe critical weed-free period is the minimum length of time during which the crop should be practicallyweed-free to avoid a yield or quality reduction. The critical weed-free period varies with crop, weed speciesand environment. The critical weed-free period concept is based on the following observations: Atthe time of field preparation and planting, the field is virtually free of weeds. Soon after, however, weedseeds brought to the surface by field preparation start to germinate.At some point, crop seedlings and weeds are large enough to compete for light, water and nutrients.Weeds usually win this competition, marking the beginning of the critical weed-free period. Young seedlingsthat have to compete with weeds for nutrients and light may form weaker plants. Weaker plants are moresusceptible to pests and diseases and may eventually give lower yields. Economic losses will occur ifweeds are not controlled. The end of the critical weed-free period is generally several weeks later whenthe crop is large enough to shade late-emerging weed seedlings or is otherwise competitive with weeds.The critical weed-free period concept, does not mean that weeds can be ignored except during thecritical period, however. If no provisions have been made to reduce weeds (e.g. by use of mulches, seesection 9.4 below), weeds may be very difficult to control by the beginning of the critical period, with orwithout herbicides. Another consideration is that weeds present after the end of the weed-free periodmay not reduce yield but can make harvest difficult.For vegetables in general a critical weed-free period is the first 4 to 6 weeks after crops are planted. Forcabbage this period can be shorter: 3 to 4 weeks after transplanting.(Peet, www6).9.4 Prevention of weed problems : some tactics“The best control is prevention” is also valid for weed management.Some tactics for weed prevention :· Crop rotation is an effective practices for long-term weed control. Crop rotation alone is usually notsufficient to control weeds, but it does introduce conditions and practices that are not favorable for aspecific weed species, reducing growth and reproduction of that species. Crop rotation provides theopportunity to plant competitive crops which prevent weed establishment. Rotation to a denselyplanted crop such as alfalfa or small grains helps prevent most annual weeds from becomingestablished and producing seed and it helps reducing populations of some perennial weeds.In addition, some weed problems are more easily managed in some crops than others becausedifferent control options may be available. Crop rotation also helps disrupt weed life cycles andprevents any single weed species from becoming firmly established.· Use uncontaminated vegetable seed and plant material.· Mulching is a very good and very commonly used method for both weed prevention and weed control.A mulch is any material placed on the surface of the soil, it can be organic matter such as straw orCabbage Ecological Guide - 2000176

Weed Managementcompost or it may be plastic sheets. A thick layer of mulch(5 cm or more) controls 90% of weeds. The mulch preventssunlight from reaching the ground. Germination of weed seedis reduced because most weed need light for germination.Even when some seed germinates, young seedlings die whenthey do not get sufficient light. In addition, a layer of mulchhelps to retain the moisture in the soil during dry periods.When organic mulch is used, it gradually rots into the soilgiving off nutrients and helping to improve the soil structure.See also section 3.5.3.· Increase planting density to shade weeds: When the crop is sown or transplanted densely, thecanopy will close quickly. Shade will prevent many weeds from germinating. In a dense crop however,chances for disease infection are higher because the humidity inside the canopy can be high.Another problem is that if weeds germinate anyway, they will be difficult to control at tight spacing.· Compost manures to reduce weed seed: animal manures may still contains weed seed.· Using cover crops to smother weeds is another widely used cultural practice. Cover crops can eitherbe planted ahead of the vegetable crop, or they can be seeded at the same time the crop is plantedto form a living mulch under the crop as it develops. Grasses, or legumes such as soybeans grownin narrow rows quickly form a complete cover, outcompeting weeds. See section 3.5.3.2 on covercrops.· Relay cropping: this means sowing seeds for the next crop before the standing crop is harvested. InBangladesh for example, common relay crops are Aman rice and Khesari (pea grass). The Khesariseeds are broadcast a week before the Aman harvest. This does not provide enough time for weedsto grow.· Weeds, and especially annual weeds, should be prevented from producing seed. When this is doneat regularly, the “store” of weed seed populations in the soil will be reduced gradually every year thatthe field is cultivated. If pulled weeds have gone to seeds, do not use them as mulch because theseeds may be spread. Instead, put them on a compost pile away from the field. If the compost isprepared properly, weed seeds are killed during the heating process of composting. See section3.5.3.1 on compost.Botanical weed control….!?Grasses, such as sorghum-sudan grass, grown as cover crops to provide weed control, may alsohave another effect. For example, when sorghum-sudangrass decomposes in the soil, a chemical isreleased that suppresses weed germination. JSome vegetables may also be sensitive to these residues, however. L(Peet, www8).9.5 How to control weedsOnce there are weeds in the field, and weed control is considered economically justified, there are manyways to get rid of them. A number of options is listed below (Peet, www6; www8; www7; www9 andwww20).177 Cabbage Ecological Guide - 2000

Weed Management9.5.1 Physical control· Handweeding is the oldest, simplest and most directway of controlling weeds. Weeding can bedone by hand or with some kind of hoe or othertool which will cut off or uproot the weeds. Hoeingis useful where there is a large area to clear ofannuals or when weeding is done around very smallplants. However, there is a risk of damaging theroots of the crop and, in dry conditions, hoeingbreaks the surface layer of the soil and increasesmoisture loss. Weeding after rain or wateringmakes it easier to remove the weeds from the ground. Perennial weeds can be eliminated by diggingthem out. This is hard work initially but once it is done, it’s done. Remove every piece of root fromperennials with easily resprouting roots, or they may form even more weeds than you started with!· Ploughing the field will bury some weeds and cut others. Prepare seedbeds immediately beforeplanting or sowing.· Mulching is an easy and very effective method of controlling weeds and keeping the ground weedfree.See prevention section above and section 3.8.4.· Allowing pigs to spend some time in the field before preparing for planting is another option. Pigs candig out and eat weeds, especially perennial weed with root stocks.9.5.2 Chemical controlThe use of herbicides (in some areas called weedicides) to control weeds isincreasing over the past years. Main reason for this is that labor costs (for manualweeding) are increasing in many countries. However, compare costs for manualweeding versus costs of applying a herbicide! It is not always cheaper to applyherbicides, especially for a crop like cabbage which covers the soil fairly quick.Generally, there are two types of herbicides (according to their mode of action):1. Contact herbicides: these kill plants on which they are sprayed. Contactherbicides are generally most effective against broadleaf weeds and seedlingsof perennials. They will usually not kill established perennials.2. Systemic herbicides: these are chemicals that are uptaken by the roots ofplants and will move within the plant to kill portions that were not sprayed.Systemic herbicides can be either sprayed on the leaves or applied to the soil (e.g. as granules).In addition, herbicides can be selective or nonselective.1. Selective herbicides kill some plant species but do not damage others,2. Nonselective herbicides will kill all plants, including cabbage plants.When considering chemical weed control, a few things are important to keep in mind:· Herbicides are unlikely to be used profitably to control weeds unless labor and cultivationcosts are high.· Herbicide performance is strongly related to environmental conditions, so not even the best herbicidesare equally effective from year to year. Herbicide performance depends upon the weather, soil conditions,and accurate application.Cabbage Ecological Guide - 2000178

Weed Management· Check details of each herbicide brand carefully: do they work selective? What weed species do theycontrol? What is the best time to apply them? What doses is recommended? How to apply them?Etc., etc. Improper herbicide use may injure plants!· Some herbicides can be dangerous to animals and humans. For example 2,4-D and Glyphosate(Round-up), commonly used herbicides, are both classified as damaging or irritating when in contactwith the human skin!· Herbicides are used to kill only weeds, however, some may be toxic N to both natural enemies andpest insects! In some cases insect populations increase, and in other cases they decrease or arenot affected. The effects can be directly toxic, with herbicides applied during oviposition or earlylarval development. They can also be indirect as with populations of the egg parasitoid Trichogrammawhich were reduced after feeding on insects which had ingested the herbicide alachlor. In otherexperiments, aphid and thrips populations increased after herbicide use. Green peach aphidspreferentially invade weed-free collard patches, probably because there were fewer predators than inmore weedy areas.(Peet, www6).Effects of herbicides on natural enemies: a study example1. Prepare hand sprayers with the herbicide to be tested.2. Select a few plants in the field. Label plants with name of treatment and spray them with theherbicide. Let leaves dry on the plant.3. Pick one or several leaves from each labeled plant and place these in jars (use gloves!).4. Collect predators, e.g. spiders or lady beetles from the field (use a small brush).5. Place predators in the jars, close the lid and place a piece of tissue paper between the lid andthe jar to avoid condensation inside.6. Check condition of predators after 8 and 24 hours.Note: instead of leaves, a piece of cloth can be sprayed with pesticides.Note: When handling pesticides wear protective clothing and wash with plenty of soap and water afterwards.· Some herbicides are known to kill or severely limit the germination and growth of beneficial fungi inthe soil, for example Beauveria bassiana, a fungus that can kill pest insects.· Some herbicides are very persistent in the soil: they can stay in the soil for a long time. They mayeven stay active in the soil until after harvest and may cause damage to the next crop.· Some herbicides can damage the crop, causing “burning” of leaves, when applied in the wrong doses(usually too high doses) or at a wrong time of the day. For example, Glyphosate (Round-up) maycause leaf burn when applied at high temperatures, in the middle of a sunny day. This herbicideinjury can be easily confused with disease symptoms.· Some herbicides are washed off during rain and loose their effectiveness.· The continued use of the same herbicide may lead to tolerance or resistance of weeds against thatherbicide. This means such a herbicide does not control those weeds anymore. This results in abuildup of weeds, particularly perennials, which are difficult to control with herbicides. The best wayof preventing the buildup of weeds tolerant to herbicides is to regularly remove them by hand and touse several brands of herbicides after each other (do not mix them!).179 Cabbage Ecological Guide - 2000

Weed Management· Generally, the best time to apply soil herbicides is when soil is moist. Do not apply herbicides on drysoil (particularly the systemic herbicides) because they may become inactive before they can killthe weeds. Not all herbicides should be applied on soil - some are to be applied on the weedsdirectly. Check labels before applying.Mixing pesticides: herbicides and insecticidesMixing herbicides with insecticides are of special concern because they often result in injury tocrop plants. Crop injury results because of chemical reactions between the insecticide and theherbicide and the effects of those chemicals on the crop. Symptoms of this injury can includestunting and yellowing.The severity of injury dependents on environmental conditions, the insecticide used, and themethod of insecticide application. It seems that rain during or prior to the application of amixture may increase the severity of injury.· When applying herbicides, it is recommended to spray infected spots only, not the whole field. Thiswill save on amount of pesticide and may save part of the beneficial population.Dependence upon herbicides alone seldom provides the most economical weed control.Good cultural and crop management practices are the backbone of any weed management program.The most desirable weed management program is one that will manage existing weeds economicallyand prevent a buildup of weed seed or tubers, rhizomes, etc. in the soil. Such a program includesintegrated use of several crop management practices which may include any of the prevention practiceslisted in 9.4.9.5.3 Biological controlWeeds, just like insects and pathogens, have natural enemies! These include insects, fungi andnematodes. Just like a cabbage plant can be attacked by an insect, a weed plant can also be attacked.Weeds are normal plants, but they are “weeds” because they grow where we do not want them.There is a lot of research being done on biological control agents for weeds. For example, there are fungithat live on certain weeds and can kill them in a short time. Applying a water solution containing sporesof those fungi may be a valuable alternative to chemical herbicides. For example, the fungus Colletotrichumgloeosporioide has been effective in controlling northern jointvetch, a plant pest in rice and soybeancrops in the USA.Insects can control weeds by feeding on seeds, flowers, leaves, stems, roots, or combinations of these,or by transmitting plant pathogens, which will infect plants.Other natural enemies of weeds include nematodes, and fish (for those weeds growing in canals, fishponds, etc.).Although there are very interesting trial data on control of weeds with natural enemies, practical fieldapplication under various conditions is still a problem. North American introductions of weed-feedingnatural enemies for example, have ranged from very successful, with a 99% reduction of the pest species,to complete failures, with the introduced species unable to become established in the new location.Weed-controlling fungi need a certain amount of humidity and may not work during the dry season.Cabbage Ecological Guide - 2000180

Weed ManagementTherefore, to date, only very few biological weed control agents are commercially available but this maychange in the near future. (www18).Related exercises from CABI Bioscience/FAO manual:2-C.7. Mulching of plant beds: organic and inorganic mulches181 Cabbage Ecological Guide - 2000

Rodent Management10RODENT MANAGEMENTSUMMARY· Rats can be an important pest of vegetables in areas where vegetables aregrown in rotation with rice, or in fields close to rice areas.· Community involvement is essential for rat control.· Rat control should be implemented continuously throughout the vegetable/riceseason.· Rat management includes prevention methods (reducing habitat and cover),mechanical methods (direct killing in rat drives or traps), biological control(enhancing predators, possibly application of pathogens), and chemical baitingmethods. All these methods should be used together. However, limit/restrictthe use of chemicals because of possible side-effects to other animals andhumans.Cabbage Ecological Guide - 2000182

Rodent ManagementRats are a common problem in agriculture, especially in rice. In areas where vegetable are grown inrotation with rice, or close to rice areas, rats can also migrate to vegetable plots and cause damage.In recent years, rats have been an increasing problem for vegetable farmers, for example in Vietnam.Several research institutes have been working on rat management more intensively in the last few years.The reasons they give for an increase of rat populations is the intensification of agriculture (more cropsper year) combined with destruction of natural habitats for rats.Many rat management programmes have been used to attempt to control rats such as rat drives, rattrapping, rat tail campaigns and burrow destruction. However, long-term rat control requires sustainedinterests and an understanding of the ways rats live. The focus of rat control must be on reducing yieldlosses. Several control methods should be used together for effective rat control.Community involvement is very important for control of rats. Proper motivation and information should besupplied through various types of participation activities and media.Community action is the key to rat management.There are several species of rat. A very common species is the big field rat (Rattus argentiventer), andthe focus of this chapter is on this rat.10.1 Ecology of the field ratAlmost everyone knows what a rat looks like, but it is the behavior of the rat which is important to know.Rats are active mostly at night. The vision of a rat is not very good, and rats may not even be able todistinguish colors. But the senses of hearing, touch, smell and taste are very good. Rats need food andshelter to survive and reproduce. Understanding how they behave to find food and shelter helps in controllingrats.FoodFood is one factor which determines rat reproduction. Field rats can reproduce when they have enoughfood from the different food groups: proteins, carbohydrates, minerals and vitamins. Reproduction isreduced substantially if there is a lack of one of these food groups in the diet of the rats. Because rats areeating food throughout the vegetable/rice season, the longer the crop season, the more rat litters areproduced. Rats often travel 200-800 m to find food.HabitatRats usually live in burrows in the ground, especially in rice bunds. But as the rice matures most rats liveand move mostly in the open (rice) fields, often making nests right in the rice plants. You can find nestsof field rats in the following places:· Straw piles, weedy bunds or the center of the fields (if fields are dry)· Burrows: Most female rats dig burrows to live when they are pregnant. Male rats rarely live in burrows.Some burrows are very simple like underground trenches with one entrance. Some burrows arerelatively complicated with many entrances and exits. Exits are covered with a thin soil layer.183 Cabbage Ecological Guide - 2000

Rodent ManagementWaterWater is a limiting factor for rat development. Rats reproduce much more in dry fields than in fields withwater. They do not reproduce when (rice) fields are flooded. During drought, there is a higher probabilityof rat outbreaks than in years when there is much rain.Rat movementsRats will often travel the same route to the same feedingplace each night. In some areas it is possible to distinguishrat trails where the rats pass very often.It is necessary to study rat movements for decision makingon suitable rat management methods. For example, insome areas with high rat populations farmers have experienced that rats are not attracted by the trapcrop, i.e., that the number of rats trapped is low. In this case, it would be helpful for farmers to know thatrats may travel to other places where there is more suitable food for their stage of development.10.2 Natural enemies of ratsThere are many animals that are natural enemies of rats. These include owls, cats, dogs, and manykinds of snakes (e.g. pythons). It is important to limit pesticide use which harm these natural enemies.For example, the use of rodenticides which rats may eat can consequently kill dogs that eat poisonedrats.10.3 Rat damage and rat population dynamicsRat development depends on many factors like food, habitat, water, and natural enemies. Among thesefactors, food is most important in determining rat population dynamics.It is important to observe fields regularly for rat damage, and use the observations in decision making onwhat to do about rats. Rat populations can increasevery rapidly. Besides the damage in the field, regularobservations can be done by farmer groups on thedevelopment of rat populations. When observationsare done on a regular base, they give farmer groupsinformation on the changes in the rat populations, evenif damage in the field is low. This can allow for timelyaction against rats, before populations get so high thatdamage in the field is occurring.Rats reduce yields of plants by direct feeding on plantparts. Methods to evaluate damage in rice fields havebeen developed, for example by IRRI (International RiceResearch Institute, the Philippines). This is notstandardized for vegetable because of the large varietyin vegetable crop, and the fact that rats usually arenot a major pest in vegetables.rat population growth in one year(from Philippine Research Institute, 1993)Cabbage Ecological Guide - 2000184

Rodent Management10.4 Rat management methodsPrevention activitiesThe best protection of the crop for rat damage is through early season control of rats. If rat damage washeavy in the previous season, rat control must begin at the beginning of the season and continue untilcrop maturity. Individual protection of fields by using a combination of plastic fences, habitat management,and baiting is possible, even if not all farmers in the area are cooperating in the rat control.Before transplanting: Cut weeds along bunds and irrigation canals, looking for rat burrows which shouldbe destroyed. Fumigation guns which use burning straw and sulfur area available in some areas for killingrats in their holes. If rat damage was very severe in the previous season, using an acute poison under theadvice of a technician in the field and village areas, or rat drives to kill rats directly during the seedbedperiod will reduce populations significantly. However, initial investments must be followed by a sustainedprogramme.After transplanting: A sustained baiting programme is the best way for farmer groups to control rats. Forsustained baiting, poisons which kill after several feedings are used. The rats must eat the poisoned baitfor rats to die. Unlike other methods, many dead rats will not be accumulated in a short time becausemany rats will die inside the burrows. This may be a problem for some farmers who usually like to see theresults of the baiting quickly. It is possible to demonstrate the effects of these poisons on captured ratsand this may be necessary to convince farmers that these poisons are useful.Community action: Group activities which emphasize participation and co-operation can be used tobegin a programme of working together to control rats. Individuals cannot control rats alone on areassmaller than several hectares. Poster making by members of farmer groups are good activities to alertother farmers to proper sustained baiting programmes and other methods to prevent the build-up of ratpopulations.It is always better for groups to participate in rat control programmes.In some areas, planting at the same time may be possible. Areas which are planted and harvestedtogether seem to have less rat damage than areas where rice (mainly rice because rats are usuallyconnected to rice areas) is always available. This is because rats can migrate from field to field in areaswith continuous planting and always find a good meal. In areas with simultaneous planting, the bestmeals are available a short period during the year. In population growth terms, more food - more rats,more continuous food - more continuous rats.A number of other rat management methods are listed below.10.4.1 Cultivation methods· Cropping pattern : Use of cropping pattern which limits food supply and habitat for rats. For example,do not grow dry crops continuously. Do rotation cropping with rice.· Timing of the season: Synchronize planting. Seeds should be sown at the same time and harvestedat approximately the same time to limit continuous food supply and habitat of rats.· Field sanitation: Cut weeds on bunds regularly, clean out bushes, level off hillocks and remove cropresidues before the season and after harvest, to limit rat habitat.· Cultivation technique: Limit high and large bunds. Irrigating fields limits and narrows down rat habitatwhich facilitates rat management.185 Cabbage Ecological Guide - 2000

Rodent Management10.4.2 Mechanical methods· Traps: Make use of all kinds of existing traps, simple to complicated ones, cheap, easy to find,effective in catching rats (live traps, snap traps, etc.). Experience sharing and training should beconducted on how to make traps, set up traps, prepare baits to increase effectivity of traps as amanagement method.· Rat drives: Use dogs to hunt rats. Combine with burrow digging, fogging and driving to catch rats. InVietnam, for example, farmers make plastic fences around fields, put the traps at the end, and makenoise so the frightened rats run into the traps.· Burrow digging, fogging and flooding: Mobilize many people as in a campaign. Conduct burrowdigging, fogging and flooding regularly combined with other methods to achieve more effect. It isnecessary to train and guide people in using these methods to protect the irrigation system.· Plastic fences: Put plastic fences around the field bunds (about 50 - 100 cm high) to prevent ratdamage. It is very easy to do but it requires much investment for materials.· Trap crop: Combine plastic fences and traps with early crop to catch rats. This method is effectivebut costly and should have the participation of the community.· Torches and scoop nets: In general, rats have poor eyesight. At night, blinded by light from the torch,they move badly. You can hit them to kill or use scoop nets to catch. This method is not popular andcan only be used by people with the necessary equipment and experience.· Sticky glue: Put the sticky glue along routes where rats often cross/pass. In the middle of the trapput baits to attract rats. This method is effective when used in houses or in store houses.10.4.3 Chemical methodRats can taste food without putting the food in their mouth because their teeth stick out so far. Rats arevery suspicious of new places and foods. When using poisons which kill after one feeding (acute), it isimportant to remember that rats will taste the food before regularly feeding. This is why acute poisoningmethods recommend putting out unpoisoned bait for 5 days before putting out poisoned baits. The rats‘learn’ that good food is readily available at a particular place, and will visit for several days eating the bait.By the time poisoned bait is placed, the rats already are happy to eat a lot. If poisoned bait is placeddirectly in the bait holder, the rats will try a little bit of the food, get a sick stomach, recover, and never goback to the bait again. It is the same as trying a new restaurant. If the food is good we visit again. If weget sick from the food, we never go back..· Acute poisons: Zinc Phosphide (20%) can be used to kill rats. This method can kill rats fast and ishighly effective at first use. But it is very poisonous for people and warm-blooded animals. Baitsmixed with poisons should be changed regularly to increase effectivity.· Chronic poison (slow action): This poison often uses anti-coagulants such as Klerat. Rats die slowlyand they are less fed up with baits. It is less poisonous for people and warm-blooded animalscompared to acute poisons.· Chemicals for fogging rat burrows/nests: Use sulfur (SO 2) and calcium carbide to fog the rat burrows/nests. Put sulfur or a piece of calcium carbide about 100 - 200 grams. Pour water and close theburrow by soil or clay. Calcium carbide or sulfur gas will kill rats. This method can be applied only toloamy soil with few cracks or in sandy soil. In the dry season it is less effective.Chemical methods are often used especially in rat campaigns or when rat populations are high becauseat that time we should reduce rat populations in a short time. However, limit use of chemicals, especiallyacute poisons, because they are harmful to people and animals!Cabbage Ecological Guide - 2000186

Rodent Management10.4.4 Biological and botanical methodsNatural enemies of rats:· Encourage and help farmers raise cats. Limit use ofrodenticides which causes death of natural enemies likecats when they eat poisoned rats.· Disseminate information on problems brought about byhunting, killing and eating natural enemies of rats suchas cats, snakes, and owls.· Advocate for laws and decrees which favor the restorationand protection of natural enemies of rats. For exampleagainst their selling and exportation.· Advocate for laws and decrees which support the implementation of management methods for rats.Microorganisms:Some microorganisms can cause infectious disease that kill rats. Advantages and disadvantages aresummarized in the following list.AdvantagesDisadvantages• Kills rats on a large scale at the same time. • Expensive.• Mostly safe for humans, other animals and • Short shelf life/storage period (the time it keepsthe environment.its potency).• Considerably reduces rat populations and its • Does not cause immediate death (rats die fromdamage over long periods of time4 - 14 days after eating) so farmers do not liketo use.• Use in the field is very much affected byweather conditionsUse of preparations with microorganisms will be more successful if the following are considered:· Avoid using in weather conditions such as scorching sun or heavy rains.· Use at the same time on a large area.· Use recommended dosage of 3 - 5 kg/ha or higher, depending on rat density. Concentrate on edgesof large fields, hillocks/earth mounds, bushes, cemeteries, etc., where rats usually dig burrows. If anunder dose is used, the effectivity cannot be guaranteed.· Should not be used more than twice a year in one place.· Apply when food is not available in the field. Rats will eat more baits.BotanicalsFollowing traditional experience, use seeds of pachyrrhizus, nux vomica for poisons. Care must be takenwhen these are used because they are very poisonous for humans and animals.(modified from: FAO - Vietnam National IPM Programme, Hanoi. Integrated Rat Management, 1998; andFAO - Vietnam National IPM Programme, Hanoi. Integrated Rat Management, Ecological Guide, 1998).187 Cabbage Ecological Guide - 2000

Key to Some Common Cabbage Insect Pests and Diseases11KEY TO SOME COMMON CABBAGEPROBLEMSAffectedplant partSeedlingSeedlingSeedlingSeedlingSeedlingSeedlingSymptoms/findingsSeedlings in nursery have small shotholesin the seed-leaves (cotyledons)and young true leavesStems of seedlings in nursery or youngplants in the field are cut through at soillevelSeedlings or young transplants have apoor growthSeedlings in nursery have damagedleaves and hearts (sometimes coveredwith caterpillars) and whole plants maydieStems are hollow at soil level or justbelow soil levelSeedlings in nursery wilt and fall oversuddenlyPossible cause(s)SeesectionFlea beetle (Phyllotreta sp.) 5.3Cutworms (Agrotis sp.) 5.4Poor soil structurePoor fertilization condition of the soilWater loggingStemborer (Melanagromyza cleomae)Webworm (Hellula undalis)Diamondback moth (Plutella xylostella)Cutworms (Agrotis sp.)Stemborer (Melanagromyza cleomae)Damping-off (Pythium sp.)Black rot (Xanthomonas campestris)Black leg (Phoma lingam)Downy mildew (Peronospora sp.)Leaf spot (Alternaria brassicae)3.43.53.95.115.75.15.45.11Seedling Seedlings in nursery have small yellowor brown spots on the leavesSeedling Upon uprooting, seedlings have Clubroot (Plasmodiophora brassicae) 8.6swollen roots and/or little galls on therootsSeedling Seedlings/transplants are stunted Stemborer (Melanagromyza cleomae) 5.11Growing Cabbage heart is deformedDiamondback moth (Plutella xylostella) 5.1pointWebworm (Hellula undalis)5.7Heart caterpillar (Crocidolomia binotalis) 5.6Growing One cabbage plant develops more Diamondback moth (Plutella xylostella) 5.1point than one headWebworm (Hellula undalis)5.7Heart caterpillar (Crocidolomia binotalis) 5.6Head Cabbage head develops brown, dry rot Head rot (Rhizoctonia solani) 8.4Head Cabbage head starts to rot, is soft and Soft rot (Erwinia carotovora) 8.3slimyLeaf Leaves are crumpled and turn yellow Aphids (Brevicoryne brassicae)5.2Whitefly (Bemisia tabaci)5.10Leaf Leaves have little “windows” where the Diamondback moth (Plutella xylostella) 5.1tissue is gone except for a transparent Webworm (Hellula undalis)5.7cuticleHeart caterpillar (Crocidolomia binotalis) 5.6LeafLeaves and head have large irregularshaped holes and a frass is visible onthe damaged leavesDiamondback moth (Plutella xylostella)Webworm (Hellula undalis)Looper (Trichoplusia ni)Cabbage white butterfly (Pieris sp.)Heart caterpillar (Crocidolomia binotalis)8.18.28.88.78.55.15.75.85.95.6Cabbage Ecological Guide - 2000188

Key to Some Common Cabbage Insect Pests and DiseasesAffectedplant partLeafSymptoms/findingsLeaves are skeletonized: only the veinsremain, the leaf tissue is all gonePossible cause(s)Diamondback moth (Plutellaxylostella)Armyworms (Spodoptera sp.)Looper (Trichoplusia ni)Cabbage white butterfly (Pieris sp.)Leaf Leaves have black or brown round spots Insect damageLeafspot (Alternaria brassicae)Black leg (Phoma lingam)Bottom rot (Rhizoctonia solani)LeafLeaves have black or brown, irregularshaped, spots or dead areasPesticide burnSunburnBlack rot (Xanthomonas campestris)Varietal characteristicNitrogen shortageLeaf Plant has a purple color on the leaves butotherwise looks normalLeaf Leaves are bluish green in color Varietal characteristicPhosphorous deficiencyPotassium deficiencySeesection5.15.55.85.9-8.58.88.4--8.2-8.9-8.98.9Stemborer (Melanagromyzacleomae) 5.11Petioles Maggots/pupae in large petioles of oldercabbage leavesStem Larvae and pupae inside stem Stemborer (Melanagromyzacleomae)Webworm (Hellula undalis)Roots Deformed roots, ‘clubs’ on the roots Clubroot (Plasmodiophorabrassicae) 8.6Whole Discolouring, wilting, roots start to rot Water logging 3.9plantWholeplantPlant wilts during warm daysWater shortageClubroot (Plasmodiophorabrassicae)Stemborer (Melanagromyzacleomae)3.98.65.11WholeplantWholeplantPlants stay very small and no headsdevelopPlant falls over, stem is rotten at the soillevelCaterpillars/larvae in the soilPupae in the soilPupae on plantsClubroot (Plasmodiophorabrassicae)Bottom rot (Rhizoctonia solaniPoor soil structure - localizedStemborer (Melanagromyzacleomae)5.115.78.68.43.45.11Black leg (Phoma lingam) 8.8Cutworms (Agrotis sp.)Flea beetle (Phyllotreta sp.)Cutworms(Agrotis sp.)Armyworms (Spodoptera sp.)Diamondback moth (Plutellaxylostella)Looper (Trichoplusia ni)Cabbage white butterfly (Pieris sp.)5.45.35.45.55.15.85.9189 Cabbage Ecological Guide - 2000

Literature and Internet Reference List12LITERATURE AND INTERNETREFERENCE LIST12.1 Literature referencesAICAF (Association for International Cooperation of Agriculture and Forestry). 1995. Diseases of tropicalvegetable crops. Tokyo, Japan.AICAF (Association for International Cooperation of Aqriculture & Forestry), 1995. Pests fo tropicalvegetable crops. Tokyo, Japan.Andaloro, J.T.; Rose, K.B.; Shelton, A.M.; Hoy, C.W.; Becker, R.F., 1983. Cabbage growth stages. NewYork’s Food and Life Sciences Bulletin 101, 1983. NYSAES, Cornell University.Atwal, A.S. 1993. Agricultural pests of India and South-East Asia. Kalyani publishers, New Delhi, India.AVRDC (Asian Vegetable Research and Development Center), 1990. Vegetable production training manual.447pp. Taipei, Taiwan.Balasubramani,V.; Swamiappan, M. (1994). Development and feeding potential of the green lacewingChrysoperla carnea Steph. (Neur. Chrysopidae) on different insect pests of cotton. Tamil Nadu AgriculturalUniversity, Coimbatore, India. Anzeiger-fur-Schadlingskunde,-Pflanzenschutz,-Umweltschutz.1994, 67: 8, 165-167.Baker, S.W., 1966. Eight years in Ceylon. Publ.Dehiwala. 221 pp.Black, L.L. 19??. Vegetable diseases, a practical guide. AVRDC, Taiwan.Bloksma, J. 1987. Ziekten en plagen in de biologische groenteteelt. Nationale raad voor LandbouwkundigOnderzoek, Den Haag, the Netherlands.CABI – South East Asian Regional Centre. 1997 (?). Dossier on Diadegma insulare (Hymenoptera:Ichneumonidae), a potential control agent for Plutella xylostella (Lepidoptera: Yponomeutidae).CABI (1996) Integrated Pest Management for Highland Vegetables. Final TA Report (1996) Philippines,managed by IIBC. 250ppCABI Bioscience UK Centre. 2000. Identification Services Report on Melanagromyza cleome.CABI Bioscience UK. TSG IPM Analyses No. 6: Impact of Farmer Field School training on natural,human and social capital: case studies from the Philippines and Kenya, CABI Bioscience.Cardona, E.V., 1997. Integrated Pest Management of the diamondback moth (Plutella Xylostella L.) incabbage in the Philippines: biological control with the use of the parasitoid Diadegma semiclausumHellen. Thesis, University of Gent, Belgium. 117 pp.Choudhury, B.C. and Hoque, M.O. (1982). Control of root-knot nematode in brinjal seed beds by heattreatments. Bangladesh Journal of Agricultural Research 7: p. 55-57Cabbage Ecological Guide - 2000190

Literature and Internet Reference ListCollingwood, E.F. et al, 1988. Vegetable production under arid and semi-arid conditions in tropical Africa.FAO Plant production and protection paper no. 89.Copping, L.G. (editor), 1998. The biopesticide manual. First edition. British Crop protection Council, UK.Department of Primary Industries (DPI), 1994. Diseases of vegetable crops. DPI, Queensland, Australia.Doty, W.L., 1990. All about vegetables. Ortho books. Chevron chemical company.Ester, A.; Broek, R.C.F.M.van den; Embrechts, A.J.M.; Kramer,C.F.G., 1993. Protection of field vegetablesagainst insect attacks by covering the crop with polythene nets. PAGV Lelystad, the Netherlands.72pp.FAO – FFS report: FFS on IPM in Tomato & Cabbage. Lao PDR. Project GCP/RAS/160/NET. Nov. 1998– March 1999.FAO – FFS report: Integrated Pest Management. Cabbage Farmers Field School in Ban Thanaleng, LaoPDR, 1997-1998.FAO - Indonesian National IPM Training and Development Program. Rice IPM. An ecological approach.Training resource text on rats, insect pests, diseases, and natural enemies of insect pests.FAO – Inter-Country Programme for the Development and Application of Integrated Pest Management inVegetable Growing in South and South-East Asia. Progress report April 1996 – Feb. 1999.FAO – TOT report: Training of Trainers course on vegetable Integrated Pest Management in brinjal (eggplant).Mymensingh, Bangladesh, 1999.FAO – Vietnam National IPM Programme, Hanoi, Updates on Vietnam national IPM programme invegetables, 1999.FAO – Vietnam National IPM Programme, Hanoi, Plant Protection Department, MARD. Vietnam NationalIPM programme. Baseline survey: vegetable production in Vietnam. March 2000.FAO - Vietnam National IPM Programme, Hanoi. Integrated Rat Management, 1998.FAO - Vietnam National IPM Programme, Hanoi. Integrated Rat Management, Ecological Guide, 1998.FAO – Vietnam National IPM Programme, Hanoi. Participatory Action Research on the Management ofSoil-borne diseases in Tomato. Results from the second season (winter 1999). Report prepared byHai Phong IPM trainers’ group and the Vietnam Nat. IPM programme.FAO – Vietnam National IPM Programme, Hanoi. The development of Vegetable IPM, Vietnam, 1994 – 2000.FAO – Vietnam National IPM Programme, Hanoi. TOT report IPM vegetables (cabbage and tomato)Hanoi 1995.FAO – Vietnam National IPM Programme, Hanoi. Training Outputs on Participatory Impact Evaluation ofIPM in Vegetables (draft report). March 2000.FAO – Vietnam National IPM Programme, Hanoi. Workshop on PAR on Management of Soil-borneDiseases in Vegetables. 10 –17 Jan. 1999.FAO – Workshop on Leafminers of vegetables in Southeast Asia. Cameron Highlands, 2-5 Feb. 1999.FAO Intercountry Programme for the development and application of IPM in Vegetable Growing in Southand South-East Asia. Regional Workshop on the use of Biocontrol Agents in Vegetable IPM. Da Lat,Lamdong province, Vietnam. 8 – 10 Sept. 1998. (FAO Dalat report, 1998)Fliert van de E. and Braun A., Farmer Field School for Integrated Crop Management of Sweetpotato : fieldguides and technical manual. International Potato Center CIP ESEAP Regional office.Flint, M.L.; Bosch, R. van den, 1981. Introduction to Integrated pest management. Plenum press, NewYork, USA.Greenwood P., Halstead A. 1997. Pest and diseases. The Royal Horticultural Society, London.Harman, G.E.; Kubicek, C.P. (editors), 1998. Trichoderma and Gliocladium, Vol. 1 and 2. Taylor&Francisltd.Hill, D.S. and Waller, J.M., 1990. Pests and Diseases of Tropical crops. Vol.2. Field handbook. IntermediateTropical Agricultural Series.Hill, D.S., 1983. Agricultural insect pest of the tropics and their control. 2 nd edition. Cambridge universitypress.191 Cabbage Ecological Guide - 2000

Literature and Internet Reference ListHoffmann, M.P. and Frodsham, A.C. (1993) Natural Enemies of Vegetable Insect Pests. CooperativeExtension, Cornell University, Ithaca, NY. 63 pp.International Programme of Chemical Safety. The WHO Recommended Classification of Pesticides byHazard and Guidelines to Classification 1996-1997. WHO/PCS/96.3.Jenkins, N.E.; Vos, J.G.M., 2000. UNEP/CABI Critical Issues Case Studies. Delivery of BiocontrolTechnologies to IPM Farmers: Vietnam. CAB International/UNEP publication 2000.Jenkins , N.E. 1 .; Grzywacz , D. 2 , 2000. Quality control of fungal and viral biocontrol agents – assurance ofproduct performance. Biocontrol Science and Technology, 2000 (in press). 1 CABI Bioscience, SilwoodPark, Ascot, UK. 2 Natural Resources Institute, University of Greenwich, Chatham, UKKar, A.C.; Khan, M.A., 1995. Homestead bio-intensive gardening and agroforestry. A technical referencemanual. LIFT project, CARE BangladeshKerruish et al., 1994Kienegger, M.; Finch, S., 1996. The effects of undersowing with clover on host-plant selection by pestinsects of brassica crops. p.108 – 114. In: Finch,S. and Brunel, E. Working Group “Integrated Controlin Field Vegetable Crops”, proceedings of het meeting. Nov. 1995.Kirk, W.D.J. (1992). Insects on cabbage and oilseed rape. U.K.Kishi M. et al. Relationship of pesticide spraying to signs and symptoms in Indonesian farmers. Scan JWork Environ Health 1995;21:124-33.Koenig, K.; Deogracias, L.; Amend, J. (1993). Mass-rearing and utilization of Diadegma semiclausum.Philippine-German Biological Plant Protection Project, BPI, the Philippines.Kumar Prabhat, 1998, field study and PAR report, BangladeshLarkcom, J., 1991. Oriental vegetables. The complete guide for garden and kitchen. John Murray Publishersltd.Lehmhus, J.; Vidal, S.; Hommes, M., 1996. Population dynamics of herbivores and beneficial insectsfound in plots of white cabbage undersown with clover. p.115 – 121. In: Finch,S. and Brunel, E.Working Group “Integrated Control in Field Vegetable Crops”, proceedings of het meeting. Nov. 1995.Loevinsohn, M. 1 ; Meijerink, G. 1 ; Salasya, B. 2 , 1998. Integrated Pest Management in Smallholder FarmingSystems in Kenya. Evaluation of a pilot project. 1 International Service for National AgriculturalResearch. 2 Kenyan Agricultural Research Institute.Loke, W.H.; Heng, C.K.; Basirun, N.; Mardi, A.R. (1992). Non-target effects of neem (Azadirachta indica)on Apanteles plutellae, cabbage, sawi and padi. Proc. of the 3rd Int. Conference on Plant Protectionin the tropics (edited by Ooi, P.A.C. et al) No.2, 108-110.Luther, G.C.; Valenzuela, H.R.; Defrank, J., 1996. Impact of cruciferous trap crops on lepideopteranpests of cabbage in Hawaii. Environmental Entomology 1996, 25:1, 39-47.MacNab A.A.; Sherf, A.F.; Springer, J.K. 1994. Identifying diseases of vegetables. The PennsylvanianState University.Matteson, P.C., 2000. Farmer Ecological Study Groups and Biological Control of Cabbage Pests inVietnam. Vietnam national IPM Programme, Hanoi.MacMillan, F., 1936. Tropical Planting and Gardening with Special reference to Ceylon.McKinlay, R.G.(editor), 1992. Vegetable crop pests. The Macmillan press ltd.Mehrotra, R.S., 1980. Plant Pathology. Tata McGraw-Hill Publishing Company ltd., New Delhi, India.Messiaen, C.M., 1992. The tropical vegetable garden: principles for imporvement and increased production,with applications to the main vegetable types. Macmillan, London, U.K. 514 pp.Moekchantuk, T. 1 ; Aquino, G. 2 ; Schmaedick, M. 2 , 1999. TOT report: Vegetable Integrated Pest Management,Training of Trainers report. 23 Nov. 1998 – 15 March 1999. Mae Suay, Chiang rai province,Thailand. 1 World Education Asia. 2 FAO IPM programme.Murakami, S., 1991. Lessons from Nature. A guide to Ecological Agriculture in the tropics. A Proshikapublication, Dhaka, Bangladesh.Cabbage Ecological Guide - 2000192

Literature and Internet Reference ListMurphy HH, Sanusi A, Dilts R, Djajadisastra M, Hirschhorn N, Yuliatingsih S . “Health Effects of PesticideUse Among Indonesian Women Farmers: Part 2: Reproductive Health Outcomes.” Agro Medicine(in press).Murphy HH, Sanusi A, Dilts R, Djajadisastra M, Hirschhorn N, Yuliatingsih,S. (2000) “Health Effects ofPesticide Use Among Indonesian Women Farmers: Part 1: Exposure and Acute Health Effects.”Journal of Agromedicine Vol 6,Issue 3.Murphy, H., 1998. Guidelines for farmer-to-farmer IPM health studies. The FAO programme for CommunityIPM in Asia. Jakarta, Indonesia.Natarajan, K. (1990). Natural enemies of Bemisia tabaci Gennadius and effect of insecticides on theiractivity. Regional Station, Central Institute for Cotton Research, India. Journal-of-Biological-Control.1990, 4: 2, 86-88.Ogilvie, L. (1969). Diseases of vegetables. London, U.K.Ooi, P.A.C., 1988. Insects in Malaysian agriculture. Tropical Press sdn.bhd. Malaysia.Ooi, P.A.C., 1992. Role of parasitoids in managing diamondback moth in the Cameron Highlands, Malaysia.pp 255 – 262. In: Talekar, N.S. (editor) Management of diamondback moth and other cruciferpests. Proc. Second International Workshop, AVRDC, Taiwan.Ooi, P.A.C., 1999. Biological control of the diamondback moth, Plutella xylostella in Dalat: a technicalreview. Sept. 1999. FAO programme for Community IPM in Asia, Jakarta, Indonesia.Ooi, P.A.C.; van den Berg, H.;Hakim, A.L.; Ariawan, H.; Cahyana, W., 1999. Farmer Field Research.The FAO programme for Community IPM in Asia. Jakarta, Indonesia.Oudejans, J.H., 1994. Agro-pesticides: properties and functions in integrated crop protection. ESCAP.Pandey B.P., 1997. Plant Pathology. Department of BotanyPostharvest Horticulture Training and Research Center (PHTRC), 1984. Village level handling of fruitsand vegetables: traditional practices and technological innovations. Department of Horticulture, Universityof the Philippines. Los Banos, Philippines.Pan Sodavy, Mam Sitha, Robert Nugent, Helen Murphy. Situational Analysis: Farmers Awareness andPerceptions on the Effect of Pesticides On their Health. FAO Community IPM Programme. PhnomPenh: Cambodia. April 2000.Parker, B.L., Talekar, N.S., Skinner, M. 1995. Field guide. Insect pests of selected vegetables in tropicaland subtropical Asia. AVRDC.Praasterink, F.M. (1996). Cabbage Integrated Pest Management. Ecological Guide. FAO- Intercountryprogramme for IPM in South and South-East Asia.Philippine Rice Research Institute, 1993. Rice production technoguide. Department of Agriculture, Philippines.Pun, L.; Karmacharya, B.B., 1998. Trainer’s manual: vegetables. Department of Agriculture, Kathmandu,Nepal.Rao,NV; Reddy,AS; Rao,KT, 1989. Natural enemies of cotton whitefly, Bemisia tabaci Gennadius inrelation to host population and weather factors. Regional Agricultural Research Station, Lam, Guntur522 034, Andhra Pradesh, India. Journal-of-Biological-Control. 1989, 3: 1, 10-12Rappaport, R., 1993. Controlling crop pests and diseases. Tropical Agricultural extension handbooks.Macmillan press ltd.Reissig, W.H.; Heinrichts, E.A., Litsinger, J.A. et al., 1986. Illustrated guide to integrated pest managementin rice in tropical asia. IRRI, Philippines.Schoubroeck, F.H.J.; Herens, M.; Louw, W.de; Louwen, J.M.; Overtoom, T., 1989. Managing pests andpesticides in small scale agriculture. Centre for Development work the Netherlands.Senewiratne, S.T.; Appadurai, R.R., 1966. Field crops of Ceylon. Publ. Colombo. 376 pp.Shepard, B.M., 2000. A microbial agent against Spodoptera exigua to eliminate dependence on chemicalinsecticides in shallots and restore natural enemy communities. Clemson Palawija IPM projectand Institut Pertanian Bogor.193 Cabbage Ecological Guide - 2000

Literature and Internet Reference ListShepard, B.M.; Barrion, A.T.; Litsinger, J.A., 1987. Friends of the rice farmer. Helpful insects, spiders,and pathogens. International Rice Research Institute. Philippines.Shepard, B.M.; Carner, G.R.;Barrion, A.T.;Ooi, P.A.C.; van den Berg, H., 1999. Insects and their naturalenemies associated with vegetables and soybean in southeast Asia.Sherf, A.F., Macnab, A.A., 1986. Vegetable diseases and their control. 2 nd edition.Singh, R.S., 1990. Plant diseases. Sixth edition. Oxford & IBH Publishing Co. Pvt. Ltd., New Delhi,India.Sivanaser, M. et al (editors), 1991. Pest Management of vegetables. Proceedings of a regional workshopon pest management of vegetables, Malaysia 8-12 Oct.1990. ASEAN Plant Quarantine Centre andTraining Institute Malaysia.Srinivasan,K.; Murthy, P.N.K.; Krishna-Murthy, P.N., 1991. Mustard plants trap major cabbage plants.Indian Farming, 1991, 40: 11, 11-12.Srnivasan, K.; Moorthy, P.N.K., 1991. Indian mustard as a trap crop for management of major lepidopterouspests on cabbage. Tropical Pest Management. 1991, 37: 1, 26-32.Tata,S.N.; Wadhawani, A.M. (editors), 1992. Handbook of agriculture. Indian council of Agricultural research,New Delhi.Theunissen, J.; Booij, C.J.H.; Lotz,L.A.P., 1995. Effects of intercropping white cabbage with clovers onpest infestation and yield. Research Institute for Plant Protection (IPO-DLO), Wageningen, Netherlands.Entomologia-Experimentalis-et-Applicata. 1995, 74: 1, 7-16Tumwine, J., 1999. Towards the development of integrated cultural control of tomato late blight (Phytophthorainfestans) in Uganda. PhD thesis, Wageningen Agricultural University, the Netherlands. 152 pp.Viet, H.T., 1998. Development of production and use of NPV (Nuclear Polyhedrosis Virus). NationalInstitute of Plant Protection (NIPP), Hanoi, Vietnam.Vos, J.G.M., 1994. Integrated Crop Management of hot pepper (Capsicum spp.) in tropical lowlands.PhD thesis, Wageningen Agricultural University, the Netherlands. 188 pp.Vos, J.G.M., 1998. Vegetable IPM exercise manual. CABI Bioscience/FAO. Volume I, II, and III.Vos, J.G.M.; Soon, L.G., 1997. Review of use of alternatives to methyl bromide for horticultural crops inAsia. METHYL BROMIDE ALTERNATIVES CONFERENCE, San Diego, 3-5 November 1997. InternationalInstitute of Biological Control (CAB International). IIBC Malaysia StationWiech, K., 1993. The influence of intercropping late cabbage with white clover and French bean on theoccurrence of pests and beneficial insects. Zeszyty Naukowe Akademii Rolniczej, no. 177, 74 pp.,Poland.Wiech, K., 1996. Intercropping as possible method of cabbage pest control in Poland. Brighton CropProtection Conference: Pests & Diseases – 1996. Volume 2: proceedings of an International Conference,Brighton, U.K. Nov. 1996. pp.675 – 678.12.2 Internet referencesPeet, M.M., PhD. Professor, Department of Horticultural Science North Carolina State University, U.S.A.Sustainable Practices for Vegetable Production in the South. Book published in 1995. WWWsite lastchanged in 1998. URL: http://www.cals.ncsu.edu:8050/sustainable/peet/Sub-pages used from this site:Cabbage, Broccoli, and Other Cole Crops. PRODUCTION PRACTICES:CABBAGE. URL: http://www.cals.ncsu.edu/sustainable/peet/profiles/ppcabage.html (reviewed on 27/09/99)www1: Types of Organic Matter Additions. URL: http://www.cals.ncsu.edu/sustainable/peet/soil/org_matt.htmlwww2: Fertility Management. URL: http://www.cals.ncsu.edu/sustainable/peet/soil/fertilit.htmlCabbage Ecological Guide - 2000194

Literature and Internet Reference Listwww3: Cabbage, Broccoli, and Other Cole Crops. PRODUCTION PRACTICES:CABBAGE. Cole cropnutrient recommendations based on soil tests. URL: http://www.cals.ncsu.edu/sustainable/peet/profiles/table9_5.html(reviewed 24/06/00)www4: Conservation Tillage. URL: http://www.cals.ncsu.edu:8050/sustainable/peet/c03tilla.html (reviewedon 21/09/99)Disease Management Practices. URL: http://www.cals.ncsu.edu/sustainable/peet/IPM/diseases/d_mgmt.html (reviewed on 20/09/99)Diseases Primarily of Cole Crops. URL:http://www.cals.ncsu.edu/sustainable/peet/IPM/diseases/cole.html (reviewed on 14/09/99).Practices and Materials Permitted in some Organic Certification Programs. URL: http://www.cals.ncsu.edu/sustainable/peet/ipm/diseases/org_cert.html (reviewed on 20/09/99)Insect pests of vegetable crops in the southern united states. URL: http://www.cals.ncsu.edu/sustainable/peet/IPM/insects/pests.html(reviewed on 11/11/99)Damping off and root rots. URL: http://www.cals.ncsu.edu/sustainable/peet/IPM/diseases/dampoff.html(reviewed on 03/11/99)www5: Cover Crops and Living Mulches. URL: http://www.cals.ncsu.edu/sustainable/peet/cover/c02cover.html (reviewed on 28/09/99)Living mulches.URL: http://www.cals.ncsu.edu/sustainable/peet/cover/l_mulch.html (reviewed on 28/09/99)www6: Weed Management. URL: http://www.cals.ncsu.edu/sustainable/peet/IPM/weeds/c07weeds.html(reviewed on 25/06/00)www7: General Practices to Control Weeds. URL: http://www.cals.ncsu.edu/sustainable/peet/IPM/weeds/gen_prac.html (reviewed on 25/06/00)www8: Specific Weed Management Practices. URL: http://www.cals.ncsu.edu/sustainable/peet/IPM/weeds/spec_pra.html (reviewed on 25/06/00)www9: Other Practices to Control Weeds URL: http://www.cals.ncsu.edu/sustainable/peet/IPM/weeds/otherpra.html (reviewed on 25/06/00)Insect management. URL: http://www.cals.ncsu.edu/sustainable/peet/ipm/insects/insecipm.html (reviewedon 06/09/99)Insect management. Biological control. URL: http://www.cals.ncsu.edu/sustainable/peet/ipm/insects/co4biolo.html (reviewed on 06/09/99)Insect Management. Insect Pathogens. URL: http://www.cals.ncsu.edu/sustainable/peet/ipm/insects/pathogen.html (reviewed on 06/09/99)Insect management. Predators and parasitoids commercially available. URL: http://www.cals.ncsu.edu/sustainable/peet/ipm/insects/par_pred.html (reviewed on 06/09/99)www10: Insect Management. Pheromones. URL: http://www.cals.ncsu.edu/sustainable/peet/IPM/insects/insecphe.html(reviewed on 06/09/99)Insect Management. Botanicals. URL: http://www.cals.ncsu.edu/sustainable/peet/ipm/insects/botan.html(reviewed on 06/09/99)Soil Management: Introduction. URL: http://www.cals.ncsu.edu/sustainable/peet/soil/soilindx.html (reviewedon 27/09/99)195 Cabbage Ecological Guide - 2000

Literature and Internet Reference ListManaging Soil Physical Characteristics. URL: http://www.cals.ncsu.edu/sustainable/peet/soil/phy_char.html (reviewed on 27/09/99)Fertility Management. Soil Testing. URL: http://www.cals.ncsu.edu/sustainable/peet/soil/fertilit.html (reviewedon 27/09/99)www11: Types of Organic Matter Additions. URL: http://www.cals.ncsu.edu/sustainable/peet/soil/org_matt.html (reviewed on 27/09/99)Management of Soil Biological Characteristics. URL: http://www.cals.ncsu.edu/sustainable/peet/soil/bio_char.html (reviewed on 27/09/99)www12: Weeden, C.R., Shelton, A.M., Hoffmann, M.P. (editors). Cornell University College of Agricultureand Life Sciences. Biological control: A Guide to Natural Enemies in North America. URL: http://www.nysaes.cornell.edu/ent/biocontrol/From this site the following sub-sites are used:Rueda, A.;. Shelton, A.M. Diamondback Moth (DBM). URL: http://www.nysaes.cornell.edu/ent/hortcrops/english/dbm.html (reviewed on 27/12/99)www13: Schellhorn, N.; Othman, N.; Smyth, R. Croci or Cabbagehead Caterpillar (CHC). URL: http://www.nysaes.cornell.edu/ent/hortcrops/english/croci.html (reviewed on 29/12/99)Ogrodnick, J. Cornell University College of Agriculture and Life Sciences. Viruses. URL: http://www.nysaes.cornell.edu/ent/biocontrol/pathogens/viruses.html (reviewed on 30/09/99)www14: D’Amico, V., NEFES - Microbial Control, Hamden, CT, U.S.A. Baculoviruses (Baculoviridae).URL:http://www.nysaes.cornell.edu/ent/biocontrol/pathogens/baculoviruses.html (reviewed on 30/09/99)Gaugler, R.. Department of Entomology, Rutgers University, New Brunswick New Jersey. Nematodes(Rhabditida: Steinernematidae & Heterorhabditidae). URL: http://www.nysaes.cornell.edu/ent/biocontrol/pathogens/nematodes.html (reviewed on 22/06/99)www15: Grafius, E.J. (1997). URL: http://www.nysaes.cornell.edu/ent/biocontrol/parasitoids/diadegma.html (reviewed on 28/06/00)www16: URL: http://www.nysaes.cornell.edu/ent/biocontrol/parasitoids/cotesia.html (reviewed on 28/06/00)www17: Chrysoperla (=Chrysopa) carnea, C. rufilabris (Neuroptera: Chrysopidae). Common GreenLacewing (=C. carnea) URL: http://www.nysaes.cornell.edu/ent/biocontrol/predators/chrysoperla.html(reviewed on 28/06/00)www18: Weed-feeders Last modified November 4, 1999. URL:http://www.nysaes.cornell.edu/ent/biocontrol/weedfeeders/wdfdrintro.html (reviewed on 28/06/00)www19: Reiners, S. Associate Professor Of Horticultural Sciences, Cornell University, New York StateAgricultural Experiment Station, Geneva, NY. (June 23, 1997) DIAGNOSING VEGETABLE PROB-LEMS. URL: http://www.nysaes.cornell.edu/pubs/press/diagnosing.html (reviewed on 28/06/00)www20: 2000 Ohio Vegetable Production Guide. Bulletin 672-00. Weed Management. URL:http://ohioline.ag.ohio-state.edu/b672/b672_9.html (reviewed on 28/06/00)www21: Sorensen, K.A., Cabbage Worm Complex. North Carolina Cooperative Extension Service,North Carolina State University. Vegetable Insect Note 12 (last checked May 1996). URL: http://www.ces.ncsu.edu/depts/ent/notes/Vegetables/veg012e/icwstg.htm (reviewed on 28/06/00)Cabbage Ecological Guide - 2000196

Literature and Internet Reference Listwww22: Shanmugasundaram, S. IPM of Diamondback Moth in South and South East Asia. The AsianVegetable Research and Development Center, Taiwan URL: http://www.nri.org/IPMForum/ipmwd/issue3/iss3uk03.htm (reviewed on 28/06/00)www23: Mitchell, E.R.; Tingle, F.C.; Navasero-ward, R.C., Impact of Cotesia plutellae (hymenoptera:braconidae) on control of diamondback moth (lepidoptera: plutellidae) in cabbage.TEKTRAN, UnitedStates Department of Agriculture, Agricultural Research Service (updated 1998) URL: http://www.nal.usda.gov/ttic/tektran/data/000007/10/0000071055.html (reviewed on 28/06/00)www24: Boucher, J.; Nixon,G. et al. University of Connecticut Integrated Pest Management Program.Preventing Bacterial Diseases of Vegetables with Hot-Water Seed Treatment. URL: http://www.lib.uconn.edu/CANR/ces/ipm/homegrnd/htms/54sedtrt.htm (reviewed 26/06/00).Boucher, J., University of Connecticut Integrated Pest Management Program. Two Common, Late-Season,Cole Crop Diseases. Reprinted from Grower vol. 93-9, p.4-5. URL: http://www.lib.uconn.edu/CANR/ces/ipm/veg/htms/coledis.htm (reviewed 06/09/99)www25: United States Department of Agriculture, Agricultural Research Service, Beltsville AgriculturalResearch Center. Commercial biocontrol products for use against soilborne crop diseases. Last modified19 May 2000. http://www.barc.usda.gov/psi/bpdl/bpdlprod/bioprod.html (reviewed on 24/06/00)www26: Vos, J.G.M., 2000. Vietnam Showcase. Pest Cabweb. Biocontrol News and Information. March2000, Volume 21 No. 1. URL: http://pest.cabweb.org/BNI/BNI21-1/TRAIN.HTM (reviewed 25/06/00).Division of Agriculture and Natural Resources, University of California. UC Pest ManagementGuidelines(HTML Revised: March 21, 2000). COLE CROPS: DOWNY MILDEW(Peronosporaparasitica). URL: http://www.ipm.ucdavis.edu/PMG/r108100311.html (reviewed on 04/04/99)Gay, J.D., Extension Plant Pathologist. The University of Georgia College of Agricultural & EnvironmentalSciences/Cooperative Extension Service. Leafy Greens and Cabbage Production. Diseases. URL:http://www.ces.uga.edu/pubcd/b1067-w.html#Mildew (reviewed 04/04/99)www27: Statewide Integrated Pest Management Project. Division of Agriculture and Natural Resources,University of California. UC Pest Management Guidelines: cole crops: leafminers. (Liriomyza spp.).URL: http://www.ipm.ucdavis.edu/PMG/r108300311.html (Reviewed: 10/02/00)Shanmugasundaram, S. Director International Cooperation Program, The Asian Vegetable Researchand Development Center, Taiwan. IPM of Diamondback Moth in South and South East Asia. URL:http://www.nri.org/IPMForum/ipmwd/issue3/iss3uk03.htm (reviewed on 27/12/99)www28: Cheah, L.H. and Page, B.B.C.; 1997 The New Zealand Plant Protection Society Incorporated.Trichoderma Spp. For Potential Biocontrol Of Clubroot Of Vegetable Brassicas. URL: http://www.hortnet.co.nz/publications/nzpps/proceedings/97/97_150.htm (reviewed on 13/01/00)www29: Biocontrol Products Registered to Control Plant Diseases in the United States. URL: http://www.agf.gov.bc.ca/croplive/cropprot/may96.htm#biocont (reviewed on 06/09/99)www30: Cogger, C.G.;Sullivan, D.M.; Duncan, S.K., 1995. Backyard composting in the 1990s. Issuedby Washington State University Cooperative Extension. U.S. Department of Agriculture. URL: http://coopext.cahe.wsu.edu/infopub/eb1784/eb1784.html (reviewed on 02/06/00)www31: New Brunswick Department of the Environment. Building a hot compost pile. URL: http://www.gov.nb.ca/environm/comucate/compost/build.htm (reviewed on 02/06/00)www32: The Composting Council of Canada, Toronto, Ontario. At Home With Composting. URL: http://www.compost.org/back.html (reviewed on 02/06/00)197 Cabbage Ecological Guide - 2000

Literature and Internet Reference Listwww33: Granatstein, D., 1997. Suppressing Plant Diseases with Compost. The Compost Connectionfor Washington Agriculture. URL: http://csanr.wsu.edu/compost/newsletter/compcon5.html (reviewedon 05/06/00)www34: Diver, S., 1998. Compost Teas for Plant Disease Control. Pest Management Technical Note,May 1998. Appropriate Technology Transfer for Rural Areas (ATTRA), Fayetteville. URL: http://www.attra.org/attra-pub/comptea.html (reviewed on 05/06/00)DOWNY MILDEW ON VEGETABLES. URL: http://ag.arizona.edu/hypermail/vegnews/0043.html (reviewedon 04/04/99)Carstens, Dr. E.B. March 19, 1996. Queen’s University at Kingston, Department of Microbiology andImmunology. URL: http://info.queensu.ca/micr/micr221/Insectvirus.html (reviewed on 14/06/00)Cabbage Ecological Guide - 2000198

PESTS & DISEASES COMMON TO CABBAGEPlate 1Fig. 1 : Crocidolomia(See section 5.6, page 94)(Source : AICAF, 1995)Fig. 2 : Hellula undalis(See section 5.6, page 96)(Source : AICAF, 1995)Fig. 3 : Black rot on cauliflower :The disease extends inwards from the leafmargins. Affected areas dry out and turn brown.Older leaves may drop from the plant.(See section 8.2, page 155)(Source : DPI, 1994)Fig. 4 : Black rot on broccoli :Leaves show infection along the leaf margins withyellow, V-shaped areas and dark veins.(See section 8.2, page 155)(Source : DPI, 1994)Fig. 5 : Black rot on cabbage :Note the typical infection through the waterpores on the leaf margin.(See section 8.2, page 155)(Source : DPI, 1994)Fig. 6 : Cabbage field seriouslyaffected with bacterial soft rot(See section 8.3, page 157)(Source : AICAF, 1995)199 Cabbage Ecological Guide - 2000

Plate 2Fig. 7 : Bacterial soft rot ofcabbage. Water soaked soft rotlesions enlarge very rapidly(See section 8.3, page 157)(Source : AICAF, 1995)Fig. 8 : Rhizoctonia bottom rot(See section 8.4, page 159)(Source : MacNab et al, 1994)Fig. 9 : Alternaria leaf spot of cabbage - largecircular lesions with concentric rings on anouter leaf(See section 8.5, page 160)(Source : Black)Fig. 10 : Field symptoms of club rot :Infected plants are stunted and wilted,particularly during the warmer part of the day.(See section 8.6, page 163)(Source : DPI, 1994)Fig. 11 : Close-up of club root infection :Spindle or club-shaped swellingsdevelop on roots.(See section 8.6, page 163)(Source : DPI, 1994)Fig. 12 : Downy mildew symptomson crucifer seedling leaves :A white fungal growth develops rapidlyunder cool, moist conditions.(See section 8.7, page 167)(Source : DPI, 1994)Cabbage Ecological Guide - 2000200

Plate 3Fig. 13 : Advanced symptoms of downy mildew :Older leaves take on a speckled appearance.(See section 8.7, page 167)(Source : DPI, 1994)Fig. 14 : Field symptomsof black leg :The disease damages theroots, causing plants towilt and collapse.(See section 8.8, page 169)(Source : DPI, 1994)201 Cabbage Ecological Guide - 2000

KEYWORD INDEXacid soil ------------------------------------------ 19AESA -------------------------------------------- 64agro-ecosystem analysis -------------------- 63Agronomic practices ------------------------- 10Agrotis ipsilon ----------------------------------- 88Agrotis segetum -------------------------------- 88Agrotis sp. --------------------------------------- 88Alternaria brassicae ------------------------- 160Alternaria leaf spot -------------------- 139, 160anatomy ----------------------------------------- 52annual weeds---------------------------------- 174antagonist ------------------------- 57, 137, 147aphid lions ------------------------------------ 113aphids --------- 82, 110, 112, 114, 119, 139mummies -------------------------------- 119armyworm --------------------------------------- 91ash --------------------------------------------- 67Bacillus thuringiensis ----- 78, 93, 102, 125bacteria --------------------------------- 137, 138Baculoviruses -------------------------------- 130Beauveria bassiana ------------------ 127, 179Beauveria sp.--------------------------------- 104Bemisia tabaci ------------------------------- 103beneficials --------------------------------------- 57biocontrol agents ------------------------ 57, 68biofumigation ----------------------------------- 38biological pesticides -------------------------- 68Biopesticides ----------------------------------- 68biorationals ------------------------------------- 68birds ------------------------------------------- 134Black leg -------------------------------------- 169Black rot--------------------------------------- 155boron -------------------------------------- 33, 143Boron deficiency ----------------------------- 171botanicals -------------------------------- 64, 150Bottom rot------------------------------------- 159boundary area planting ----------------------- 21Brevicoryne brassicae----------------- 82, 128broadleaf weeds ----------------------------- 175Bt ------------------------------------------- 125ABcabbageorigin --------------------------------------- 4cabbage heart caterpillar -------------------- 94cabbage looper -------------------------------- 98cabbage white butterfly -------------------- 100calcium ---------------------------------------- 143calendar spraying --------------------------- 150Chili --------------------------------------------- 67Chrysopa carnea ---------------------------- 112Chrysopa rufilabris -------------------------- 112climate ------------------------------------------- 11Clubroot --------------------------------------- 163coccinellid beetle ---------------------------- 110Coenosa sp. ---------------------------------- 108compensation ------------------------------ 8, 55Compost ---------------------------- 17, 24, 154advantages ------------------------------- 24decomposition time -------------------- 27disadvantages --------------------------- 25disease control -------------------------- 27how to prepare -------------------------- 25how to use ------------------------------- 29tea ----------------------------------------- 29temperature ------------------------------ 26thermometer ----------------------------- 27Cotesia glomerata ------------------ 101, 122Cotesia marginiventrus --------------------- 122Cotesia plutellae ------------------------ 77, 122Cotesia rubecula ----------------------------- 122Cover crops ------------------------ 21, 29, 177critical weed-free period -------------------- 176Crocidolomia binotalis----------------- 94, 128crop defenders --------------------------------- 57crop development ------------------------------- 5Crop rotation --------------------- 48, 145, 176crop visitors ------------------------------------- 56cropping calendar ------------------------------ 6cutworm ----------------------------------------- 88damping-off ----------------------------------- 152decomposition --------------------------------- 24CDCabbage Ecological Guide - 2000202

deficiency symptoms ----------------------- 143defoliation study -------------------------------- 8Diadegma insulare --------------------- 77, 120Diadegma semiclausum -------------- 76, 120Diadegma sp. --------------------------- 59, 120Diadromus collaris --------------------- 77, 124Diaeretiella rapae ----------------------- 83, 119diagnosing problems ----------------------- 142diamondback moth 75, 120, 122, 124, 128disease culture ------------------------------ 144Disease ecology ----------------------------- 136disease management -------- 136, 141, 145Disease spread ------------------------------ 139disease triangle ------------------------------ 140disease zoo----------------------------------- 144Downy mildew -------------------------------- 167Drainage ----------------------------------------- 45Green manure ---------------------------------- 30ground beetle ---------------------------------- 111growth stage ------------------------------------ 56HaNPV ------------------------------------------ 130Harvest ------------------------------------------- 48health -------------------------------------------- 71Hellula undalis --------------------------------- 96herbicides -------------------------------- 68, 178herbivores --------------------------------------- 55Heterorhabditis sp. -------------------------- 133hover flies -------------------------- 59, 83, 114Humus ------------------------------------- 19, 23Hybrid variety ----------------------------------- 11hyperparasitism ------------------------------- 114Hecology ------------------------------------------ 51economic threshold level -------------------- 63Encarsia sp. ---------------------------------- 104entomopathogenic fungi -------------------- 127Entomophthora sp. -------------------------- 128Epilachna sp.--------------------------------- 110Erosion control ---------------------------------- 21Erwinia carotovora -------------------- 157, 158ETL --------------------------------------------- 63Fertilizerchemical ---------------------------- 21, 33foliar --------------------------------------- 34inorganic ---------------------------------- 33recommendations for cabbage ------ 35Fertilizer deficiency ------------------------- 170Fertilizer management ----------------------- 22field preparation -------------------------------- 41flea beetle ---------------------------------------- 85flooding field ------------------------------------ 45fuel oil -------------------------------------------- 68fungi ------------------------------------- 137, 138fungicides ------------------------------------- 149EFinsect cage ------------------------------------- 61insect zoo --------------------------------- 54, 56insect-pathogenic fungi.-------------------- 127insecticidal soaps ----------------------------- 68Insecticides -------------------------------------- 69Inter-Country Programme --------------------- 3Intercropping ------------------------------------ 46IPM ---------------------------------------------- 2Irrigation ----------------------------------------- 45kerosene ---------------------------------------- 68lacewing --------------------------------- 104, 112lady beetle ------------------------ 83, 104, 110Leaf spot --------------------------------------- 160Leptosphaeria maculens -------------------- 169life cyclecomplete---------------------------------- 53incomplete ------------------------------- 53light trap ----------------------------------------- 62Lime --------------------------------------------- 19Living mulch ------------------------------------ 30IKLGgarlic -------------------------------------- 67, 150germination -------------------------------------- 13Gliocladium virens --------------------------- 148granulosis virus ------------------------------ 130MMacronutrients --------------------------------- 22magnesium ----------------------------------- 143magnesium deficiency --------------------- 171Manure ------------------------------------------- 31nutrient contents ------------------------ 31203 Cabbage Ecological Guide - 2000

Marigold ----------------------------------------- 66Melanagromyza cleomae ------------------ 107Metarhizium sp. ------------------------------ 128microbials --------------------------------------- 68micronutrients ---------------------------------- 22microorganisms -------- 19, 21, 23, 24, 137Microplitis sp. ---------------------------------- 93milk ------------------------------------------- 150mineralization ---------------------------------- 24Mixed cropping --------------------------------- 46monitoring --------------------------------------- 51mouthparts -------------------------------------- 52mulching--------------- 21, 40, 44, 106, 176mummies -------------------------------------- 119mushrooms ----------------------------------- 149mustard ------------------------------------------ 47Nnatural enemiesaugmentation ---------------------------- 59conservation ----------------------------- 59purchase ---------------------------------- 60release ------------------------------------ 60natural enemy efficiency --------------------- 58neem --------------------------------------------- 65nematodes ----------------------- 57, 138, 140entomopathogenic -------------------- 132net house --------------------------------------- 61neutrals ------------------------------------ 16, 56nicotine ------------------------------------------ 65nitrogen ----------------------------- 22, 33, 143nitrogen deficiency -------------------------- 171nitrogen excess ------------------------------ 171non-systemic pesticides --------------------- 70NPV -------------------------------------- 92, 130advantages/disadvantages ----------- 131Nuclear polyhedrosis virus ---------------- 130Nursery management ------------------------ 36nutrient consumption ------------------------- 48nutrient deficiency --------------------------- 143nutrient toxicity ------------------------------ 143OOP --------------------------------------------- 12Open pollinated variety ----------------------- 12organic matter ---------------------------------- 23Organic mulch ---------------------------------- 32Paecilomyces sp. -------------------- 104, 128Pparasite ---------------------------------------- 117parasitoids ------------------------------- 57, 117pathogens ------------------------ 57, 124, 137Peacilomyces fumosoroseus -------------- 105perennial weeds ------------------------------ 174Peronospora parasitica -------------------- 167Pest management strategy ------------------ 3pesticide poisoning --------------------------- 71pHraising soil -------------------------------- 20pheromone trap -------------------------------- 62Phoma lingam ------------------------- 139, 169phosphorous deficiency --------------------- 171phosphorus ------------------------ 22, 33, 143Phyllotreta sp. ---------------------------------- 85physiological disorders --------------- 138, 170Pieris brassicae ---------------------- 100, 122Pieris rapae ---------------------------- 100, 122pigs ------------------------------------------- 135pitfall trap ---------------------------------------- 62plant compensation --------------------------- 86planting density -------------------------------- 43planting time ------------------------------------ 36Plasmodiophora brassicae --------- 139, 163Plutella xylostella ------------------------------ 75Polyculture -------------------------------------- 46Post-harvest ------------------------------------ 48potassium -------------------------- 22, 33, 143potassium deficiency ----------------------- 171praying mantid ------------------------------- 116predators --------------------------------- 57, 110appetite test ----------------------------- 58pyrethroids -------------------------------------- 66pyrethrum --------------------------------------- 66Pythium sp. ---------------------------- 139, 152resistance --------------------------------------- 72resistant variety -------------------------------- 12resurgence -------------------------------------- 72Rhizoctonia solani --------------------------- 159Rodent management ------------------------ 182root systems ----------------------------------- 23rotenone ----------------------------------------- 66Sanitation --------------------------------------- 42Secondary nutrients -------------------------- 22seed treatment --------------------------------- 13biological --------------------------------- 15botanical ---------------------------------- 15RSCabbage Ecological Guide - 2000204

chemical ----------------------------------- 14hot water ---------------------------------- 14seed-borne diseases ------------------------- 13Seedbank ------------------------------------- 175SeNPV ------------------------------------ 92, 130SlNPV ------------------------------------ 92, 130soap --------------------------------------------- 68Soft rot ---------------------------------- 157, 158Soil --------------------------------------------- 16Soil conservation ------------------------------ 21Soil health--------------------------------------- 24soil imbalance ----------------------------------- 23soil infection ------------------------------------- 17soil pH -------------------------------------- 17, 18Soil sterilizationbiological --------------------------------- 38soil sterilization -------------------------- 18, 36soil structure ----------------------------------- 17soil test ------------------------------------------ 23soil testing kit ---------------------------------- 19soil type ----------------------------------------- 17Soil water-holding capacity ----------------- 24soil-borne diseases -------- 13, 17, 48, 139prevention -------------------------------- 18solarization ------------------------------------- 37Sowingflat field ------------------------------------ 39in pots ------------------------------------- 40precision ---------------------------------- 40raised seedbed -------------------------- 39spacing ----------------------------------- 43, 177spiders ----------------------------------------- 115Spodoptera exigua ---------------------------- 91Spodoptera litura ------------------------------ 91Spodoptera lituralis --------------------------- 91Spodoptera sp. --------------------------------- 91Steinernema bibionis ------------------------- 90Steinernema carpocapsae ---------------- 133Steinernema riobravis ----------------- 90, 133Steinernema sp. ------------------------------ 133Steinernema spp. --------------------------- 109stemborer ------------------------------------- 107sticky trap-------------------------------- 63, 105Storage ------------------------------------------ 48sub-soil ------------------------------------------ 38sulphur ----------------------------------------- 143susceptible variety ---------------------------- 12syrphid flies ----------------------------------- 114systemic pesticides -------------------------- 69tobacco ------------------------------------------ 65tolerance level ---------------------------------- 63tolerant variety --------------------------------- 12transplanting ------------------------------------ 42trap crop ----------------------------------- 47, 79Trichoderma ---------------------------------- 136Trichoderma harzianum -------------------- 148Trichoderma sp. -------- 148, 153, 159, 165seed treatment -------------------------- 15Trichoderma viride --------------------------- 148Trichoplusia ni --------------------------- 98, 122Undersowing ------------------------------------ 33variety selection ------------------------------- 11Verticillium lecanii ---------------------------- 105Verticillium sp. ------------------------ 104, 128viruses ---------------------------------- 137, 138UVWWater management --------------------------- 45webworm ---------------------------------------- 96Weed control -------------------------- 175, 177Weed management ------------------ 173, 175weed-free period concept ------------------ 176weedicides ------------------------------------ 178weeds -------------------------------------------- 59whitefly ---------------------------------- 103, 139WHO pesticide classification --------------- 70Why this guide? --------------------------------- 1wirestem --------------------------------------- 159Xanthomonas campestris ---------- 139, 155yellow sticky trap ------------------------------ 63Zoophthora radicans ------------------- 78, 128XYZTerraces ----------------------------------------- 21T205 Cabbage Ecological Guide - 2000

Cabbage Integrated Pest Management : An Ecological Guide.

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