50 Years of Herbicide Resistance in Kansas: How We Got Here and What’s Next
By Lonnie Mengarelli Ag and Natural Resources Agent – Southwind District
This year marks 50 years since Kansas documented its first herbicide-resistant weed. That 1976 discovery—triazine-resistant kochia along railroad rights-of-way—seemed like an isolated case at the time. Today, herbicide resistance is one of the most serious challenges facing Kansas farmers. As we recognize this anniversary, it’s worth looking back at how resistance evolved, where we stand now, and what it will take to manage it moving forward.
Herbicide resistance is the ability of a weed population to survive an herbicide dose that would normally kill it. This is different from herbicide tolerance, which is a weed’s natural, built-in ability to withstand a certain herbicide.
Resistance develops when herbicide use selects for rare genetic traits that allow certain plants to survive and reproduce. Over time, those traits become more common in the field.
Kochia set the stage for herbicide resistance problems in Kansas. After atrazine-resistant kochia was identified in 1976, resistance spread rapidly thanks to the plant’s tumbling growth habit and widespread use of triazine herbicides in crop fields.
Another milestone came in 1987, when kochia populations resistant to ALS-inhibiting herbicides (Group 2) were confirmed. Since then, kochia has added resistance to dicamba and fluroxypyr (Group 4) and glyphosate (Group 9), making it one of the most challenging weeds in the High Plains.
Palmer amaranth and waterhemp—two aggressive pigweed species—have become the state’s most notorious resistant weeds.
Palmer amaranth resistance to Group 2 herbicides was identified in 1993, and the species has since developed resistance to at least six herbicide groups. Palmer amaranth is the only Kansas weed with documented resistance to HPPD herbicides (Group 27), and resistance to Group 15 herbicides has been confirmed just south of the Kansas border. More recently, dicamba-resistant Palmer amaranth was identified for the first time.
Waterhemp has a similar story. By 1995, Kansas populations were already resistant to both Group 2 and Group 5 herbicides, and glyphosate resistance followed in 2006. Both Palmer amaranth and waterhemp are dioecious, meaning they cross-pollinate readily—and that genetic shuffling speeds up the spread of resistance traits.
As of 2025, 16 weed species in Kansas have confirmed herbicide resistance. Thirteen of these are broadleaf weeds; three are grasses. Many are winter annuals that emerge in the fall and cause problems the following spring.
The largest number of resistant species—13—is associated with Group 2 herbicides. Glyphosate resistance (Group 9) ranks second, with six resistant species identified.
The busiest years for new resistance confirmations were 2013 and 2021, each with six new cases. Only two new cases have been added since 2021, but researchers caution that this does not signal a slowdown—only that resistance often goes undetected for several years before being confirmed.
Herbicide resistance will continue to evolve. It is a natural biological process, but it is accelerated when the same herbicide modes of action are used repeatedly. Kansas farmers have faced this steady march for five decades, and the path forward will require more than relying on new chemistry.
The most effective long-term strategy is integrated weed management—diversifying herbicide programs, incorporating cultural and mechanical practices, and reducing seed production by surviving weeds. More details on these strategies will be covered in a follow-up article.
Lonnie Mengarelli is a K-State Research and Extension Agriculture agent assigned to Southwind District. He may be reached at [email protected] or 620-223-3720
K-State Research and Extension is an equal opportunity provider and employer.
Reference:
Heap, I. 2025. International Herbicide-Resistant Weed Database.
For additional information, see the 2025 Chemical Weed Control for Field Crops, Pastures, and Noncropland or contact your local K-State Research and Extension office.
Patrick Geier, Weed Scientist, Garden City
Yasir Parrey, Assistant Scientist, Weed Extension Lab
Sarah Lancaster, Extension Weed Management Specialist