Free herbicide-resistant weed screening for Michigan soybean producers

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Glyphosate-resistant weeds continue to be of growing concern for growers, particularly since several different glyphosate-resistant weeds have been identified in the states surrounding Michigan. Weeds that often escape control in Roundup Ready fields include horseweed (marestail), common ragweed, giant ragweed, and common lambsquarters. While not all weeds that escape control are resistant, it is important to identify the cause of the lack of control. Currently, horseweed is the only weed that we have confirmed resistant to glyphosate in Michigan. Other weeds, for example common ragweed and giant ragweed, have been confirmed resistant to glyphosate in other states in the Midwest.

Confirming herbicide-resistant weed populations is the first step of any resistance management program. Confirmation of resistance will provide growers with the knowledge to implement the best possible management strategies with the ultimate goal of preventing or limiting the spread of herbicide-resistant weeds.

Because of the many benefits that glyphosate offers Michigan soybean growers and the high potential for selecting for glyphosate resistance, MSU’s Diagnostic Services with funding provided by the Michigan Soybean Promotion Committee has an ongoing herbicide resistance screening program that was started in 2003. Diagnostic Services will conduct free glyphosate-resistance screening for soybean producers that feel they may have glyphosate-resistant weeds. All samples will be screened for glyphosate resistance as well as resistance to ALS-inhibiting and triazine herbicides.

How do I get my weeds screened for resistance?

The process is very simple. All you need to do is collect seedheads from mature plants in late summer to early fall following appropriate guidelines listed in the weed resistance submittal form available at MSU Extension county offices and agricultural retail facilities. Please document herbicide and cropping histories. Clip several seedheads and place them in a paper bag (do not use a plastic bag). These samples can be mailed to:

Michigan State University
Diagnostic Services
101 Center for Integrated Plant Systems
East Lansing, MI 48824-1311
Attn: Resistance Screening

Note: both common and giant ragweed seeds are found in the leaf axils. They are not found at the very top of the plant. If you have any questions about field criteria or seedhead collection, please call Christy Sprague at 517-355-0271 ext. 1224 or by email at

Dr. Sprague's work is funded in part by MSU's AgBioResearch.

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