Free screening for glyphosate-resistant weeds in Michigan

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 are a growing concern for Michigan producers. Horseweed (marestail) was first reported resistant to glyphosate in 2007 in Michigan. While glyphosate-resistance has been fairly limited in Michigan, bordering states have reported wide-spread resistance of horseweed and giant ragweed and more localized glyphosate-resistance of common ragweed and waterhemp. Confirming herbicide-resistant weed populations is the first step of any resistance management program. Verification will provide producers with the knowledge to implement the best possible management strategies with the ultimate goal of preventing or limiting the spread of herbicide-resistant weeds. Glyphosate offers Michigan growers many benefits and is used frequently in several crops. The high frequency of use in glyphosate-resistant (Roundup Ready) corn, soybean and sugarbeet increases the selection pressure for glyphosate-resistant weeds. If glyphosate-resistant weeds become wide-spread in Michigan, this technology’s usefulness is at risk. Diagnostic Services at Michigan State University has conducted and will continue to conduct free glyphosate-resistance screening for Michigan growers. This free glyphosate-resistance screening has been funded by the Michigan Soybean Promotion Committee through the Michigan soybean checkoff program.

If you think that you have a glyphosate-resistant weed species, please consider submitting a sample to MSU Diagnostic Services, 101 Center for Integrated Plant Systems, East Lansing, Michigan 48824 (attn: Christy Sprague) or contact your local extension office. Samples will also be screened for ALS- and triazine-resistance. Sampling consists of collecting seedheads from mature suspected-resistant plants. Clip off several seedheads and place them in a paper bag.

Note: both common and giant ragweed seeds are found in the leaf axils. They are not found at the very top of the plant. Please use Diagnostic Services sample submittal forms when sending in samples. If you have any questions about field criteria or seedhead collection, please contact Christy Sprague at 517-355-0271 x.1224 or

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

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