Growers need to think “rotation” to prevent pesticide resistance

Reduce the development of resistant pests by rotating modes of action in your crop production chemicals, as well as rotating your crops.

Look at any farm management newspaper and magazine and over the last year and you will most likely see an article on pest resistance development. Whether it is glyphosate-resistant horseweed or Palmer amaranth, Bt and rotation-resistant western corn rootworms, fungicide-resistant Cercospora in sugar beets, or frogeye leafspot in soybeans, common pests are adapting their biology and behaviors in an effort to be able to survive on the nearly endless resource our agricultural crops represent. Despite the wide variety of resistance issues that we face, there are some management commonalities that we can use on-farm to help reduce the incidence of pesticide resistance.

Rotation of modes of action for crop chemicals

When you rotate modes of action in your crop production chemicals whether it is herbicides, fungicides or insecticides, you stand a much better chance in reducing development of resistant pests in your fields. Michigan State University Extension in conjunction with other land-grant institutions has the right tools to help you select crop chemicals to achieve this goal.

MSU specialists Christy Sprague and Martin Chilvers highlighted resources that growers can use to develop crop protection programs that rotate modes of action at the MSU Pest Management Programs across Michigan this winter. Sprague discussed how you can use the Corn and Soybean Herbicide Mode of Action Chart to make sure that the herbicide programs you are considering actually have alternating modes of action from season-to-season. Chilvers introduced the excellent resource Field Crop Fungicides for the North Central United States, which discusses how to use the FRAC codes to rotate fungicide modes of action. Both of these excellent tools can help you to quickly identify common modes of action in herbicides and fungicides and to design pest control strategies that reduce the chance for resistance development.

Crop rotation

Continuous crops often lead to rapid buildups of pests, which can help resistance gain a foothold in fields. Rotating crops can change-up the pest complex, as well as change the type and amount of crop residue that can harbor insect and disease pests, and allow for a wider array of active ingredients to be used in pest control. Cash crop rotations that include wheat can also change the available window for controlling weeds through herbicide and tillage, and you can get paid for your efforts. Crop rotation generally helps to boost corn yields 15 percent over continuous corn production.

Evaluation of how well a pesticide application worked is an important step in effective pest management. Post-application scouting to evaluate control, injury and escapes is the best way to identify if you have pesticide resistance developing on your farm. The trick in identifying resistance is to locate “strong” escapes that you cannot explain in the field. This is somewhat easier for weeds than for insects or diseases because they are less mobile. Keep in mind that there may be only a few survivors in a field following a pesticide application.

Not all escapes are due to pesticide resistance. In the vast majority of cases, weather-related stress, insect or weed interactions, incorrect dosage, inadequate coverage or weather events following application play important roles in pesticide failures. Each incidence warrants investigation.

If you are concerned about what you are seeing in your fields, don’t hesitate to visit with MSU Extension educators or specialists. If you need help with pest identification or would like to ascertain if herbicide resistance is truly an issue, consider submitting a sample to MSU Diagnostic Services. You can contact your local Extension office or me via email if you suspect resistance. Be sure to capture digital images to help tell your story when you can.

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