Weed Seed Screening Helps Detect Herbicide Resistance in Michigan

By Andi Anderson

As harvest begins and planning for the next growing season takes shape, Michigan farmers are encouraged to watch for weeds that survive herbicide applications. These escapes may signal herbicide resistance, a growing challenge in crop production.

To help farmers confirm resistance, Michigan State University Plant & Pest Diagnostics provides bioassay screening of weed seeds during the fall and winter months.

The process involves cleaning seeds, treating them for dormancy, growing them in greenhouse conditions, and exposing them to as many as seven herbicides. A known susceptible population is always included to verify results.

Depending on the species, results are typically available by March. New cases of resistance not previously confirmed in Michigan require additional testing.

The Michigan Soybean Committee is sponsoring free screening for key problem weeds, including pigweeds, ragweeds, horseweed, and common lambsquarters, for soybean growers.

For other species or non-soybean systems, the cost is $90 per sample. Farmers planning to submit unlisted species should first contact MSU to ensure a known susceptible population is available for comparison.

Most weed seeds mature by October, and samples should be submitted by mid-November to allow for winter testing. Farmers should follow MSU’s “Tips for Collecting Weed Seeds” guide to ensure seeds are mature, sufficient in quantity, and properly packaged.

At least five plants per sample are recommended. A submission form must accompany each sample and can be found on the Plant & Pest Diagnostics website.

Testing results help confirm whether herbicide resistance is present or if other factors contributed to weed escapes. With resistance becoming more common across the state, timely screening can make a big difference in planning herbicide programs for the upcoming season.

For more details, farmers can access MSU’s History & Map of Herbicide-Resistant Weeds in Michigan online. This program is supported by USDA’s Crop Protection and Pest Management Program.

Photo Credit: michigan-state-university-msu