By Erin Hill
As we begin harvest season and make plans for the next year, consider any weeds that have escaped control with herbicides. If you are seeing survival in weeds that used to be controlled by your herbicide program, herbicide resistance could be an issue. Michigan State University Plant & Pest Diagnostics offers bioassay screening of weed species for herbicide resistance starting in the fall and winter months of each year. This screen can confirm resistance and rule out the many other factors that could contribute to weed escapes.
To screen for resistance, seeds are cleaned from dried plant material, treated for dormancy, grown in the greenhouse and treated with up to seven different herbicides (herbicides screened are based on the species, cropping system, suspected resistance, and quantity of seedlings). A known susceptible population is tested alongside all samples to verify results. The duration of the process depends on the species, but results are usually available no later than March. New incidence of resistance (i.e., not previously confirmed in Michigan) require additional testing.
The Michigan Soybean Committee will again be sponsoring the testing of select species (i.e., pigweeds/amaranths, ragweeds, horseweed and common lambsquarters) for Michigan soybean growers.