By Liz Stahl and Angie Peltier, Extension Educators in Crops
Herbicide resistance in weeds is an increasing problem for farmers across Minnesota. Only 18 percent of farmers surveyed at Private Pesticide Applicator Recertification workshops in MN in 2025 indicated they did not suspect they had herbicide-resistant weeds on the land they farmed (Stahl, et. al, 2025).
If you have had weeds escape herbicide control and suspect resistance rather than a suboptimal herbicide application, MN farmers have an opportunity to confirm herbicide resistance in some specific situations through genetic screening. University of MN Extension is partnering with North Dakota State University and the National Agriculture Genotyping Center (NACG) located in Fargo, on a multi-year survey to track herbicide resistance using genetic screening methods. The survey involves some scouting, proper weed ID, and collection of a couple of leaves to screen for resistance.
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| Waterhemp in a field. Photo: Liz Stahl |
If you have had weeds escape herbicide control and suspect resistance rather than a suboptimal herbicide application, MN farmers have an opportunity to confirm herbicide resistance in some specific situations through genetic screening. University of MN Extension is partnering with North Dakota State University and the National Agriculture Genotyping Center (NACG) located in Fargo, on a multi-year survey to track herbicide resistance using genetic screening methods. The survey involves some scouting, proper weed ID, and collection of a couple of leaves to screen for resistance.
What types of resistance can be detected?
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| Fig 1. These weed species and herbicide group combinations can be tested (or tests are in development) through DNA analysis |
The genetic testing being offered is limited to known DNA changes linked to resistance so it will therefore be unable to detect metabolic resistance in a population (which is increasingly being found as the source of resistance in the state). At the time of this posting, kochia, Palmer amaranth, and waterhemp can be tested for DNA markers linked to Group 2 (ALS Inhibitors; e.g. First Rate, Pursuit, Raptor), Group 9 (i.e. glyphosate), and Group 14 (PPO Inhibitors; e.g. Flexstar) herbicide resistance. While previous surveys in MN using greenhouse trials for verification have demonstrated that herbicide resistance to multiple herbicide groups in waterhemp is widespread, particularly to Group 2 and Group 9 herbicides, less is known about the status of herbicide resistance in kochia in MN.
Redroot pigweed and Powell amaranth can also be tested, but only the Group 2 test works on these pigweeds. Green Foxtail and Wild Oat samples are also being asked for, as testing for Group 1 (Accase Inhibitors; e.g. Select Max, Post) and Group 2 resistance is hoped to be available soon.
It is asked that one collection kit be used per farming operation, although there is some flexibility for operations that cross into multiple counties. Sampling should target weeds that survived herbicide applications (PRE or POST) and/or from areas where large weed patches have been a persistent issue.
Anthony Hanson Morris Regional Extension Office
Ryan Miller: Rochester Regional Extension Office
Claire LaCanne: Andover Regional Extension Office
Liz Stahl: Worthington Regional Extension Office
Eric Yu: Farmington Regional Extension Office
Dave Nicolai: Farmington Regional Extension Office
Matt Pfarr: Mankato Regional Extension Office
Angie Peltier: Northwest Research & Outreach Center, Crookston
Debalin Sarangi: Department of Agronomy & Plant Genetics; St. Paul
Further Questions or Waiting for Results? — Contact the NAGC at research@genotypingcenter.com.
Redroot pigweed and Powell amaranth can also be tested, but only the Group 2 test works on these pigweeds. Green Foxtail and Wild Oat samples are also being asked for, as testing for Group 1 (Accase Inhibitors; e.g. Select Max, Post) and Group 2 resistance is hoped to be available soon.
How will results be used?
Results from this survey will be used to help generate county-level maps to give a broader picture of where resistant traits can be found across the landscape. This information can ultimately help inform decision makers, and on-farm weed control strategies.Who can help with the survey?
Anyone in the agricultural community can help with the survey. However, proper weed identification is critical. For example, kochia tests will completely fail on a waterhemp sample. The U of MN Weed Identification site is a useful weed identification resource.It is asked that one collection kit be used per farming operation, although there is some flexibility for operations that cross into multiple counties. Sampling should target weeds that survived herbicide applications (PRE or POST) and/or from areas where large weed patches have been a persistent issue.
What is the cost?
Testing is being provided for FREE by the MN Soybean and Wheat Research & Promotion Councils on a first-come, first-served basis, for the first 175 samples provided during this pilot survey. If funds run out for FREE testing, NAGC will notify submitters and let them decide whether to run samples for a fee billed to the submitter ($75-$195/sample). No submitter will be charged without being contacted first.How can I get a sampling kit?
Each kit contains the needed sampling form and further details for sample collection and submission. Kits will be available upon request and at various U of MN field days and events. You may also contact one of the following University of MN Extension personnel to make arrangements for obtaining a kit:Anthony Hanson Morris Regional Extension Office
Ryan Miller: Rochester Regional Extension Office
Claire LaCanne: Andover Regional Extension Office
Liz Stahl: Worthington Regional Extension Office
Eric Yu: Farmington Regional Extension Office
Dave Nicolai: Farmington Regional Extension Office
Matt Pfarr: Mankato Regional Extension Office
Angie Peltier: Northwest Research & Outreach Center, Crookston
Debalin Sarangi: Department of Agronomy & Plant Genetics; St. Paul
Further Questions or Waiting for Results? — Contact the NAGC at research@genotypingcenter.com.
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