5 Fungicide Factors to Consider

Thinking of applying a fungicide? Here are five considerations that can help you get the most bang for your buck.

1. Label information

A number of fungicides these days have active ingredients from different fungicide classes like triazoles and strobilurins (Headline Amp, Quadris Xtra). That's good, as premixes containing different fungicides from different action modes can widen the disease-control spectrum. Just make sure you know what is in them and the percentage of active ingredient for each compound, says Daren Mueller, Iowa State University Extension plant pathologist.

"We are seeing repackaged products, similar to what is going on in the herbicide market," says Mueller. "You need to know how effective each product is for the targeted disease."

2. fungicide classes

"Triazole fungicides are the most widely used fungicide class in the world," says Mueller. These locally systemic fungicides move up and down the plant but not in the leaf.

Triazole fungicides (Folicur, Domark) inhibit an enzyme that plays a role in fungi sterol production. "These are the building blocks of membranes," says Mueller. Triazole fungicides result in abnormal fungal growth and eventual fungi death.

Meanwhile, strobilurin (Headline, Quadris) and SDHI fungicides are locally systemic and adversely impact fungal respiration. These can have beneficial benefits to plant physiology outside of disease control, often labeled as Plant Health or Plant Performance.

SDHI fungicides (Solatenol, Endura) are locally systemic. Fungicides with this mode of action inhibit fungal respiration in a different manner than the strobilurin fungicides.

3. Curative vs. preventive.

Curative fungicides are often thought of working on fungal diseases after they are present, while preventive fungicides are thought of working before disease is present.

However, all fungicide types work best before disease is present. "All have protective functions – even triazoles," says Mueller. "They form a (plant) barrier and prevent infection by stopping spores from germinating."

Curative fungicides have activity against early fungal infection when applied 24 to 48 hours after infection.

"They do not cure or remove disease lesions that are present," he says. "They can stop or slow infection that has occurred, but they cannot remove lesions." Triazole fungicides are often associated with curative ones. That often hinges on disease type, though.

"Strobilurin fungicides have more curative properties on some rust pathogens compared with triazoles," he says.

4. failed fungicides

Fungicide-resistant fungi often come to mind when fungicides fail. There are other reasons for failure, says Mueller.

• Incorrect diagnosis. "Make sure you have fungal disease in the field," says Mueller. Fungicides won't work if Goss's wilt infests the field, as it is a bacterial disease.
• Improper sprayer rate and calibration. "If you spray at a lower rate, you might certainly be increasing the chances of selecting for a resistant fungal strain," says Mueller. "Pay attention to the label."
• Improper application timing. "Ideal application timing can differ," says Mueller. "It depends on the weather and the amount of inoculum out there. It is a moving target."

5. Scouting

Walking your fields can help uncover disease and prompt an immediate decision. Seeing disease in the field can mean different things, though. Some diseases like gray leaf spot often move up the canopy, while others may come in from outside the field. However, a fungicide application can halt further infection.