Debalin Sarangi, Extension Weed Scientist, Navjot Singh, Weed Science Graduate Student, Lisa Behnken, Research Specialist and Retired Crops Extension Educator, Ryan Miller, Crops Extension Educator, and Tom Peters, Extension Weed Scientist
This article documents the first confirmed case of glufosinate-resistant waterhemp in Minnesota, and likely the second case in the United States, following the initial report from Illinois in early 2026. Glufosinate is a non-selective, contact herbicide (site-of-action Group 10) used primarily in glufosinate-resistant crops. Glufosinate is the active ingredient in products, including Liberty® 280 SL, Liberty® ULTRA, Surmise®, Cheetah® Pro, and Interline®.
Glufosinate inhibits glutamine synthetase (GS), a vital enzyme that helps combine glutamate and ammonia to form glutamine, and acts as a key regulator of nitrogen metabolism. Inhibition of GS in sensitive plants causes an excess accumulation of ammonia in plants, and as a result, severe foliar injury within a few hours following glufosinate application occurred. Although glufosinate was commercialized in the United States and Canada in 1993-94, its use increased dramatically after 2010, largely driven by the need to control glyphosate-resistant weeds (Fig. 1a & b).
In 2023, we received a lead from a farmer in Dodge County, MN, about a waterhemp control failure where a full labeled rate of glufosinate had been used. Waterhemp seeds from this farm were collected in the fall of 2023, and a series of greenhouse and field trials were conducted to confirm and characterize the resistance to glufosinate. As shown in the bottom image (Fig. 2), waterhemp plants sprayed with glufosinate (Liberty 280 SL at 32 fl oz/A + 1.5 lbs/A AMS, applied at 15 GPA) at a height of less than three inches exhibited injury to the top portion of the stem (shoot apical meristem); however, plants survived by regrowing from the lateral growing points developing new growth from axillary buds. This regrowth pattern was consistent among resistant plants.
Greenhouse dose-response bioassays indicated that this waterhemp population was approximately 2.8- to 3-fold resistant to glufosinate when compared to a known susceptible population. This level of resistance is relatively low compared to what has been reported for glyphosate in waterhemp; however, labeled application rates of glufosinate may still result in incomplete control. In field experiments conducted at the farm, Liberty 280 SL applied at 32 fl oz/A provided approximately 60% control. The same waterhemp population demonstrated reduced sensitivity to atrazine (Group 5), imazethapyr (Group 2), 2,4-D (group 4), glyphosate (Group 9), and fomesafen (group 14).
This research was coordinated by graduate student Navjot Singh with funding support from the Minnesota Soybean Research and Promotion Council. Further research on the mechanism of resistance, conducted in collaboration with Drs. Franck Dayan and Todd Gaines from Colorado State University, suggests that the resistance in not due to a target-site mutation, but rather a non-target site mechanism. Additional information on the resistance mechanism will be provided in the future.
The extent of glufosinate resistance in Minnesota is currently unknown. However, given recent confirmations and increasing suspicion of resistance across the Midwest, it is likely that this is not the only waterhemp population with glufosinate resistance in the state. It is imperative that we are good stewards of herbicide tools and consider adoption of non-chemical weed management strategies. It is important to start the season with a ‘strong’ (multiple effective sites of action and full labeled rate for your soil type and crop) pre-emergence residual herbicide program to reduce the number and size of plants exposed to post-emergence applications. In addition, mixing and rotating herbicide sites of action can still help delay further resistance development. When applying glufosinate, always follow label recommendations for rate, additives, and application timing (weed height and crop stages). For more details, refer to our previous extension articles on best practices for glufosinate use and don’t break glufosinate.
Also, listen to this recent Strategic Farming webinar, where Extension Weed Scientists Drs. Rodrigo Werle (UW-Madison) and Debalin Sarangi (UMN) discussed about the waterhemp management strategies, including the use of pre-emergence residual herbicides, multiple sites of action, and non-chemical strategies. The summary of this webinar can be found here.
This article documents the first confirmed case of glufosinate-resistant waterhemp in Minnesota, and likely the second case in the United States, following the initial report from Illinois in early 2026. Glufosinate is a non-selective, contact herbicide (site-of-action Group 10) used primarily in glufosinate-resistant crops. Glufosinate is the active ingredient in products, including Liberty® 280 SL, Liberty® ULTRA, Surmise®, Cheetah® Pro, and Interline®.
Glufosinate inhibits glutamine synthetase (GS), a vital enzyme that helps combine glutamate and ammonia to form glutamine, and acts as a key regulator of nitrogen metabolism. Inhibition of GS in sensitive plants causes an excess accumulation of ammonia in plants, and as a result, severe foliar injury within a few hours following glufosinate application occurred. Although glufosinate was commercialized in the United States and Canada in 1993-94, its use increased dramatically after 2010, largely driven by the need to control glyphosate-resistant weeds (Fig. 1a & b).
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| Fig. 1a. Agricultural use of glufosinate in the United States. Source: https://water.usgs.gov |
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| Fig. 1b. Glufosinate use by year and crop in the United States. Source: https://water.usgs.gov |
Baseline waterhemp resistance screening survey (2020-2021)
Results from Minnesota indicated that waterhemp populations with multiple herbicide resistance were already spreading across the state. At four separate locations we confirmed that waterhemp populations were resistant to six herbicide sites of action (Group 2, 4, 5, 9, 14, and 27), leaving glufosinate (Group 10) as the only effective post-emergence option for controlling these populations. However, with the confirmation of glufosinate resistance in waterhemp, we are now at a point where we may discover a population of waterhemp with no effective post-emergence herbicide options.Glufosinate resistance confirmation
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| Fig. 2. Waterhemp plants surviving glufosinate application in the field at 21 days after treatment by regrowing from the lateral growing points. Photo: Dr. Debalin Sarangi |
This research was coordinated by graduate student Navjot Singh with funding support from the Minnesota Soybean Research and Promotion Council. Further research on the mechanism of resistance, conducted in collaboration with Drs. Franck Dayan and Todd Gaines from Colorado State University, suggests that the resistance in not due to a target-site mutation, but rather a non-target site mechanism. Additional information on the resistance mechanism will be provided in the future.
The extent of glufosinate resistance in Minnesota is currently unknown. However, given recent confirmations and increasing suspicion of resistance across the Midwest, it is likely that this is not the only waterhemp population with glufosinate resistance in the state. It is imperative that we are good stewards of herbicide tools and consider adoption of non-chemical weed management strategies. It is important to start the season with a ‘strong’ (multiple effective sites of action and full labeled rate for your soil type and crop) pre-emergence residual herbicide program to reduce the number and size of plants exposed to post-emergence applications. In addition, mixing and rotating herbicide sites of action can still help delay further resistance development. When applying glufosinate, always follow label recommendations for rate, additives, and application timing (weed height and crop stages). For more details, refer to our previous extension articles on best practices for glufosinate use and don’t break glufosinate.
Also, listen to this recent Strategic Farming webinar, where Extension Weed Scientists Drs. Rodrigo Werle (UW-Madison) and Debalin Sarangi (UMN) discussed about the waterhemp management strategies, including the use of pre-emergence residual herbicides, multiple sites of action, and non-chemical strategies. The summary of this webinar can be found here.
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