Rotating sites of action to post-pone or prevent herbicide resistance

MSU pest management meeting surveys reveal that Michigan field crop growers are committed to rotating sites of action to post-pone or prevent herbicide resistance.

Michigan State University Extension field crop weed control specialist Christy Sprague placed considerable emphasis at the MSU Extension Winter Crop Management Programs on talking about methods growers can use to reduce the chances that herbicide-resistant weeds will develop in their operations. Sprague introduced participants to the "Take Action Herbicide Classification Chart,” a tool published by the United Soybean Board that helps growers quickly identify the site of action of various herbicides that are labeled for use in various production systems.

The goal of this sheet is to easily identify the sites of action for individual and pre-mixed herbicides so that weed control programs can be designed that rotate between sites of action, or the targeted metabolic pathways that the herbicides attack. Rotation of the site of action can greatly reduce the chance that herbicide-resistant weeds will gain a foothold in grower’s fields.

The tool utilizes both color and herbicide site of action group numbers to help growers be able to see how closely various herbicide options are related. This tool can be used in conjunction with Sprague's annually updated MSU Extension Bulletin E-434, “Weed Control for Field Crops,” to select programs for corn, soybeans, small grains and other crops within the crop rotation sequence that are effective at controlling the weed species that are present in the field and that rotate between sites of action to reduce the chance for herbicide-resistant weed development.

Post-program surveys indicate that 78 percent of the participants at these meetings agree that rotating herbicide sites of action is important for preserving the weed control management tools that they count on, and will begin or continue to rotate between sites of action in the herbicide programs they use on their operations. Of the program participants from all locations except Alpena, Mich., 44 percent said they are currently managing at least one herbicide-resistant weed on their operation.

Special thanks to the Michigan Corn Marketing Program, Michigan Soybean Promotion Committee and Michigan Wheat Program for helping to sponsor the meeting series and keep registration costs at the $20 level. They also provided the Weed Control Guide for participants at these meetings.

For up-to-date information on weed control issues throughout the growing season and other weed control resources, visit Sprague's website at

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