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Avoiding Fungicide Resistance in Corn

Best practices to keep disease and chemical resistance at bay

Like most corn farmers, growers across the Southeast rely on fungicides for disease control in their crops. Over time, however, certain diseases can build up resistance to fungicides, rendering these crucial treatments ineffective. Fortunately, growers can avoid certain practices and employ some measures to reduce the effects of fungicide resistance.

Bad Habits

Resistance occurs when a few individual fungal spores mutate and lose their sensitivity to a chemical, eventually giving the disease the ability to take over. Certain farm practices increase the likelihood of this happening, and corn growers should do their best to avoid them. 

North Carolina State University Extension Plant Pathologist Steve Koenning advises growers to only apply fungicide when necessary. "The more chemicals you put down, the greater the chance of resistance," Koenning says. When applying fungicide, check the label to make sure the coverage is correct, as well as the timing. If the fungus has already begun reproduction, growers often have to make another chemical application, which increases the chance of resistance.

Other factors can contribute to resistance, such as reducing the rate of fungicide and going longer between sprays to save costs. "These practices tends to promote resistance," says Koenning. "Increasing the intervals between sprays or lowering the dosage can lead to the disease spreading more rampantly, thus requiring the need for more chemicals."

Growers can also fall into the routine of choosing the same chemical chemistries for each application. "I would advise corn growers to never use the same chemistry twice in a row," Koenning states. Fortunately for corn farmers, there are many different options for them to choose from, with numbers indicating the classification of chemicals right on the label. In addition, companies continue to develop new formulas as their customers have expressed concerns with the growing problem of resistance.

Prevention is Key

Koenning advises southern growers to be proactive and spray on time. "In all cases, spray preventively and in a timely manner," Koenning states. "When you get behind with your spraying program, it's hard to catch up."

Fungal disease problems are unpredictable. Keeping up with neighbors, local Extension offices and university publications can help keep growers apprised of any news of disease problems in their area. "If your neighbor's crops are fighting disease, go ahead and make an application on your corn," advises Koenning. "The best time to spray is the day before the fungus arrives."

In addition, growers can choose resistant seed varieties if they have faced disease problems before and want additional protection, says Koenning. "Choosing a resistant chain is always tied to yield and costs but can be well worth it if there has been a problem in the past."

In situations where a resistant seed is not available, such as in a no-till sweet corn crop, Koenning advises an application of fungicide before flowering and then again two weeks later. As resistance is not currently available for forage and sweet corn in no till and continuous corn hybrids, resistance preventive measures become all the more essential.

For more information on fungicide resistance and its impacts on disease control, please consult your local Southern States Agronomy Professional or local Extension agency.

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