Argemone mexicana L.

Mayotte : Argemone mexicana flowers from May to November and fruits from July to January.
New Caledonia: The seeds of A. mexicana remain dormant in the hot season to germinate in early April. Flowering occurs in the cool season, followed by fructification which runs until dry season.

Argemone mexicana is an annual species. Reproduction occurs by seed. It is estimated that a single plant can produce up to 30 000 seeds per year (60 to 90 capsules per plant, 300 to 400 seeds per capsule). Seeds of Mexican Poppy usually fall close to the parent plant. Seeds are readily dispersed by moving water, especially where plants grow in riparian habitats and on terrain where erosion and runoff occurs. Contaminated soil, fodder, vehicles and the fur and hooves of livestock are also vectors for transport of Mexican Poppy seed. The seeds can also be dispersed by birds.

Comoros: Argemone mexicana is a ruderal species observed in abundance in all dry regions of low altitude of the three islands.
Madagascar: weedy species that grows during the off-season (winter) in flood-recession crops or on flood-prone dried land-cultivated or not (usually fertile land: vertisols and alluvial soils) in the West and Southwest regions (low altitude). A. mexicana prefers moderately rich to rich soils in dry areas.
Mauritius: Ruderal plant and weed in sugar cane fields, some vegetable crops and fallow. It grows especially in the dry zone of the island.
Mayotte: Argemone mexicana is an exotic species naturalized in some very degraded xerophilous stations. It is mainly found in urban areas in Petite-Terre.
New Caledonia: A. mexicana grows in poor soils.
Reunion: A. mexicana is a common plant, mainly during the winter months in crops and fallow land, except in very wet area. It occurs in cultivation, mostly on the South and West area. It grows on bare or undeveloped areas left after tillage.
Seychelles: A. mexicana is a species of clearings and abandoned places. It is rarely abundant. 
South Africa: Mostly observed on vegetables field around the lowveld part of Limpompo province on the escarpment of Blydespoort river. Also present on river banks and as ruderal plant.

Toxicity

Argemone mexicana is toxic to mammals and birds. Cases of poisoning are rare in cattle, but the seeds can be ingested by accident in contaminated hay (digestive and respiratory symptoms)

Global Weediness

It is prolific in disturbed sites and competes with agricultural crops and indigenous species. This plant contaminates crop seed. Spiny fruits and leaf tips can adhere to the wool of sheep. The seeds are poisonous to humans and livestock.

Local Weediness

South Africa: Prohibited weed (CARA 2002 ? Category 1 Proposed legislation: NEMBA ? Category 1b); problematic in many crops, new dams and cleared site. It is poisonous, can result in fatality to livestock and humans. A problem in KwaZulu-Natal and the lowveld of Mpumalanga and Limpopo Provinces.

Global harmfulness

Argemone mexicana is a serious invasive species of crops and pastures in many countries (Argentina, India, Mascarene Islands, South Africa, Australia).
 
Local harmfulness

Comoros: Argemone mexicana is a common weed in young cassava cultivations.
Madagascar: A. mexicana is common in dry conditions, it can invade the bare surfaces. It is harmful on small plants (young culture). This is a serious weed for flood-recession crops (cool season): lima beans, corn, vegetables crops, sweet potatoes. Its serrated and prickly leaves make it very difficult to harvest in fields whether they are slightly or non weeded especially for the Cape peas and cassava. The plant is not palatable by animals.
Mauritius: A weed that competes moderately to strongly with young culture when present in large numbers.
New Caledonia: Introduced in the early 19th century, it is mainly present in dry areas where we see the flowering, the "explosion" of settlements in riverbeds. It can be invasive in degraded pastures, in areas of bare soil.
Reunion: Species infrequent, present in 16 % of cultivated land and scarce, with an average cover of 7-15%. It can occasionally cause problems. It propagates easily, it can occupy any area left bare or not replanted quickly after tillage. In gardening (Fr> 30%) it can become a significant constraint if it is not controlled at the beginning of culture.
Seychelles: Species with low harmfulness.
South Africa: Argemone mexicana proliferates on disturbed sites, competing with agricultural crops and native species. This plant contaminates crop seeds. The spiny fruits and leaf tips can adhere to sheep wool. The seeds are toxic to humans and livestock. It is found in KwaZulu-Natal and in the lowlands of Mpumalanga and Limpopo provinces.

Local management

Madagascar: weeding (without gloves) is difficult (very prickly leaves). Argemone mexicana is tolerant to classic pre-emergence herbicides, (except diuron), but to 2,4 D (young stage only) or glyphosate (young or old stadium). It is important to prevent its spread, and for that we should prevent it from graining, and to keep the plots covered.

New Caledonia: The priority is to prevent the germination and spread of Argemone mexicana. Isolated plants can be removed manually or mechanically buried. The plants already in seeds must be handled with care. The largest infestations can be controlled by cultural methods (plowing and rototillers) and rotary-cultivator for early stage but natural regeneration by planting is abundant, it will have to renew these operations several times until all the seeds in the soil are depleted. For older stands but before flowering, rotary-cultivator followed by a herbicide spray or targeted (depending on the by density) on the 15-day regrowth (2,4-D, picloram + 2,4-D ). Germination may be spread, it will be important to retreat late seedlings. 

Reunion Island:

(Doses are expressed in commercial products) - 2014

Data acquired in Reunion on the effectiveness of herbicides in the context of the sugarcane herbicide network by eRcane Network with funding from the ODEADOM and ONEMA.
Action led by the French Ministry of Agriculture, food and forest, with financial support from the National Agency for Water and Aquatic Environments, on the finance issued from the tax for the pollution diffused, attributed to the finance of the Ecophyto plan.

Herbarium pictures ReCOLNAT: https://explore.recolnat.org/search/botanique/simplequery=Argemone%2520mexicana