University of Minnesota Extension weed scientists are asking farmers to participate in another weed survey.

Debalin Sarangi, U-MN Extension weed scientist, and graduate student Navjot Singh in an Oct. 5 blog shared results from a 2020 weed survey and asked that growers collect and submit weed seeds again this season.

In 2020, the scientists received about 30 waterhemp samples, mostly from southern Minnesota. They grew them in the greenhouse and conducted resistance screening. They found that the majority of waterhemp populations were resistant to ALS-inhibiting herbicides (e.g., Pursuit, Raptor and Classic) and glyphosate.

They reported that the results also showed that 14% and 15% of waterhemp populations were resistant to atrazine and PPO inhibitors (e.g., Flexstar), respectively. If at least 40% of plants survive a 3X labeled dose of a certain herbicide, that population is considered to be resistant.

The researchers noted that two populations from Carver and Olmsted County showed resistance to four herbicide sites of action, significantly reducing herbicide choices for farmers. These populations survived the 3X application of glyphosate, Raptor, Atrazine, and Flexstar or Callisto (a HPPD inhibitor).

In three populations, 7% to 14% of waterhemp plants have survived the 3X dose of 2,4-D-choline (Enlist One), showing that the less-sensitive individuals to 2,4-D are present in Minnesota. Given the results, growers are advised to take a diversified management approach to slow down the resistance evolution.

Seed samples requested

Sarangi and his team are again collecting weed seed samples this year. They ask that growers follow the steps given for sample collection and submission:

Samples may also be submitted to local Extension educators in crops.

For questions, contact Sarangi at [email protected]

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