Tom Peters, Extension sugarbeet agronomist and weed scientist, Debalin Sarangi, Extension weed scientist, Liz Stahl, Extension educator-crops, and Jeff Stachler, Extension cropping systems specialist, North Dakota State University.
I see broadleaf weeds standing tall above the canopies of low-growing crops, including sugarbeet, dry bean and soybean, as I travel across the countryside. Many of these escape weeds are waterhemp. Waterhemp has been prolific in eastern North Dakota and Minnesota in 2025 for several reasons, including an abundance of rainfall in the second half of summer.
We can’t just hope that Liberty resistance will not happen. Waterhemp has a long history of being resistant to herbicides. Waterhemp has developed resistance to herbicides across multiple sites of action (SOA), including the following:
It provides excellent information on the best ways to use Liberty herbicide. We emphatically state, “spray small weeds.” Yet I hear reports from coffee shops and my own observations of herbicides being applied well past flowering.
The images below are from a field I traveled past on multiple occasions in 2022. The soybean field has waterhemp towering over the canopy in August. Ironically, the field displayed symptoms on waterhemp I would categorize as from a SOA 10 herbicide. I was later informed the application was made to reduce seed formation. The quickest way to wreck glufosinate is incomplete kill on big weeds. Don’t do it!
I close with a comment I read on social media sometime ago. The tenure of the conversation was about weed escapes in soybean. I read, “Liberty will not hurt your beans. Sprayed some rescue in August. Not an ideal time but things happen.” I get it. However, I also feel it is my responsibility to be a guardian of one of the few remaining waterhemp control herbicides. If we lose the effectiveness of this chemistry, what tools will we have left?
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| Waterhemp surviving late-season application of Liberty in a Meeker County field. Photo: Debalin Sarangi |
Producers and other agricultural stakeholders have also noticed and have called my extension office looking for quick-fix solutions. Most are interested in a herbicide treatment that will make waterhemp go away or at minimum, reduce seed set. The logical candidate herbicides asked about include glufosinate, the active ingredient in Liberty/Liberty Ultra or maybe a premix of 2,4-D and glyphosate, marketed as Enlist Duo. Many farmers are also interested in tank mixing glufosinate (Liberty) with 2,4-D (Enlist).
Don't do it!
The short answer is don’t do it. Don’t make these applications on 4- to 5-foot tall waterhemp. The most obvious reason is that it's an off-label application! Why? Because our crops are flowering, setting pods and in many cases filling seed, using soybean as an example.The Liberty label states that it can be applied to LibertyLink soybeans up to the R1 (bloom) growth stage. R1 is the reproductive growth stage indicating the beginning of flowering. At this stage, at least one open flower is visible on the main stem of the soybean plant. This means once you see an open flower on any node on the plant, Liberty applications must stop.
Enlist can be applied through the R1 stage or up to the R2 stage or full bloom stage. The R2 stage is characterized by the presence of at least one open flower on one of the two uppermost nodes of the main stem. Finally, Roundup can be applied through the R2 stage, meaning that once you reach the R3 stage or the beginning of pod development, applications must stop.
Why the label restrictions? Are they about soybean tolerance? Maybe not, but important reasons for label restrictions include avoiding regulatory concerns, potential environmental issues, and potential issues with pesticide residue levels at harvest.
Want to preserve the efficacy of Liberty herbicide? Mix it up!
I will give you another reason. The thought of Liberty-resistant waterhemp would be devastating to producers. I have long advocated for a systems approach to weed management. That is, different sites of action (SOA) in the crops planted in a rotation in a field. Simply stated, mix it up: use herbicides from different families alone and in mixtures, soil applied and postemergence. Include non-chemical tactics where feasible (e.g. inter-row cultivation, cover crops, narrow rows) as well.We can’t just hope that Liberty resistance will not happen. Waterhemp has a long history of being resistant to herbicides. Waterhemp has developed resistance to herbicides across multiple sites of action (SOA), including the following:
- ALS inhibitors (Group 2)
- auxin mimics (Group 4)
- photosystem II inhibitors (Group 5)
- EPSPS inhibitors (Group 9)
- PPO inhibitors (Group 14)
- very long-chain fatty acid synthesis inhibitors (Group 15)
- HPPD inhibitors (Group 27).
I don’t want to see the onset of glutamine synthetase inhibitors (Group 10) (Liberty) resistance. Consider too that it is very rare to find a waterhemp population resistant to only one SOA these days, multiple resistance (up to 6 SOAs has been reported in MN) is widespread across our states.
Be a good steward of Liberty herbicide
A year ago, several of us contributed to an article in Crop News called Best practices for using glufosinate (Liberty) herbicide. I encourage anyone using glufosinate to read the article again.It provides excellent information on the best ways to use Liberty herbicide. We emphatically state, “spray small weeds.” Yet I hear reports from coffee shops and my own observations of herbicides being applied well past flowering.
The images below are from a field I traveled past on multiple occasions in 2022. The soybean field has waterhemp towering over the canopy in August. Ironically, the field displayed symptoms on waterhemp I would categorize as from a SOA 10 herbicide. I was later informed the application was made to reduce seed formation. The quickest way to wreck glufosinate is incomplete kill on big weeds. Don’t do it!
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| Four- to five-foot waterhemp in soybean field in Northwest MN August, 2022. Photo: Tom Peters |
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| Waterhemp in same soybean field after possible Liberty application in Northwest MN, August, 2022. Photo: Tom Peters |
For more information
Additional resources regarding crop growth stage cutoffs and postemergence herbicide applications:- Soybean Growth Stage Cutoffs: https://blog-crop-news.extension.umn.edu/2025/06/updated-soybean-growth-stage-cutoffs.html
- Corn Growth Stage Cutoffs: https://blog-crop-news.extension.umn.edu/2025/06/updated-corn-growth-stage-cutoffs-for.html
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