Herbicide-resistant weeds are widespread in Minnesota and several reports of weed control failure following herbicide applications were reported recently. Therefore, testing weed populations for herbicide resistance is important to plan future weed management practices more efficiently.

The University of Minnesota Extension has started an initiative to screen the weed populations collected from agronomic crop fields for herbicide resistance. Extension is requesting stakeholders from Minnesota to submit the seed samples for weeds which survived the pre-emergence and/or post-emergence herbicide treatments.

The study is targeting common weed species including, but not limited to, pigweeds (waterhemp and redroot pigweed, etc.), giant ragweed, common ragweed, common lambsquarters, marestail (or horseweed), kochia, foxtails and barnyard grass.

The resistance screening is free.

To submit the samples, first locate weed escapes. The samples can be collected from a field with a history of having herbicide-resistant weeds, or from a random field where the weed escapes are present. Check the seedheads for the presence of mature seeds. Depending on the weed species, seeds may occur on the seedhead at top, or on the branches, or at the leaf axils. Male plants don’t produce seeds.

Clip the seedheads of a weed from five or more plants per field and put them in paper bags. DO NOT USE plastic bags, as they promote mold growth.

Seal the paper bags carefully and ship them to Debalin Sarangi, 411 Borlaug Hall, 1991 Upper Buford Circle, St. Paul, MN 55108. You can also bring the samples to a local crops Extension educator if there is one present in your county.

For each sample, please include the submitter’s name and contact email; the GPS coordinate of the collection site, or township and zip cod, if GPS coordinates are not available; the crop name and the weed name; names of the herbicides applied this season (if available) and field history (if available). Information may include crop rotation, crop traits, and herbicide treatments, etc. for the past years

The U of M Weed Science team will grow the weed seeds in the greenhouse at the St. Paul campus and screen them for possible herbicide resistance. The dose response bioassays will be conducted on selective populations. Some of the samples will also be tested in a laboratory using molecular techniques.

Results are usually available within six months after submission. Sometimes it may take longer, depending on the weed species and the number of samples received.

Herbicide-resistant weeds in Minnesota will be documented and distribution maps for the common weeds will be created.

Weed management recommendations will be provided.

Future surveys will focus on the weed species shift and the evolution of multiple herbicide resistance.

If you have questions, contact Debalin Sarangi, Extension weed scientist, at dsarangi@umn.edu or (612) 625-8130.

This article was submitted by University of Minnesota Extension.