Herbicide-resistant waterhemp and ragweeds survey help requested

Navjot Singh, Graduate student, and Debalin Sarangi, Extension weed scientist

Figure 1. Waterhemp plant surviving
Enlist One application at 6 pt/A after
28 days after treatment in the
greenhouse.

Herbicide-resistant weeds are threatening agronomic crop production in Minnesota (Figure 1). In 2020, we received about 30 waterhemp samples - mostly from southern MN - and the greenhouse resistance screening results showed that the majority of waterhemp populations were resistant to ALS-inhibiting herbicides (e.g., Pursuit, Raptor, and Classic) and glyphosate. 

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, we consider that population to be resistant.

Figure 2. Distribution of multiple herbicide-resistant
waterhemp populations in Minnesota.

Two populations from Carver and Olmsted County showed resistance to four herbicide sites of action, significantly reducing herbicide choices for farmers (Figure 2). These populations have 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 (Figure 1). Therefore, a diversified management approach should be taken to slow down the resistance evolution.

Seed samples requested

Please follow the steps below for sample collection and submission:

• Select the fields with lower than expected weed control from herbicide applications (avoid sampling plant escapes due to lack of spray coverage)
• Collect the seedheads from at least 10 mature (black color seeds), female waterhemp plants, or 20 mature (brown seeds) ragweed plants and place the samples in paper bags. DO NOT mix the seeds of different species – please bag them separately!
• Fill out this submitter’s form and send it along with the samples.
• The samples can be mailed directly to the UMN’s St. Paul campus:
• Attn: Debalin Sarangi
  411 Borlaug Hall
  1991 Upper Buford Circle
  St. Paul, MN 55108

Samples can also be submitted to our local Extension Educators in crops: https://extension.umn.edu/crop-production/contacts-crop-production

Questions?

Any questions or concerns should be directed to:

Dr. Debalin Sarangi, Extension Weed Scientist
Email: dsarangi@umn.edu

This research is funded by the Minnesota Soybean Research & Promotion Council.