50 Years of Herbicide Resistance in Kansas — K‑State Urges Integrated Weed Management

Kansas State University marks 50 years since the state's first recorded herbicide resistance case — atrazine‑resistant kochia in 1976. Resistance has since been documented in 16 weed species across Kansas, and many now resist multiple herbicide classes. K‑State recommends integrated weed management—combining cultural, mechanical and chemical tactics—and directs readers to its Nov. 13 Agronomy eUpdate for full resistance details.

08:50 AM, 11/27/2025Environment

50 Years of Herbicide Resistance in Kansas — K‑State Urges Integrated Weed Management

This year marks the 50th anniversary of the first documented case of herbicide resistance in Kansas. Kansas State University researchers say the problem, first observed in atrazine‑resistant kochia along railroad rights‑of‑way in 1976, has grown more widespread and complex across the state.

Weed species with reported resistance

Since 1976, resistance has been documented in 16 species. Below are the species and the year each was first reported in Kansas:

Bushy wallflower — first documented in 2005
Cheat — first documented in 2007
Common cocklebur — first documented in 1997
Common ragweed — first documented in 2007
Common sunflower — first documented in 1996
Flixweed — first documented in 2006
Giant ragweed — first documented in 2006
Henbit — first documented in 2014
Horseweed/Marestail — first documented in 2005
Japanese brome — first documented in 2007
Kochia — first documented in 1976
Palmer amaranth — first documented in 1993
Redroot pigweed — first documented in 1995
Shattercane — first documented in 1996
Waterhemp — first documented in 1995
Wild buckwheat — first documented in 2020

K‑State researchers note that many of these species have evolved resistance to multiple herbicide chemistries, making control more difficult in both agricultural fields and home landscapes. For a detailed list of which species are resistant to which herbicide groups, K‑State points to its Agronomy eUpdate from Nov. 13.

Recommended approach: integrated weed management

To slow the spread and reduce the impact of resistant weeds, K‑State recommends adopting an integrated weed management approach that combines multiple tactics rather than relying on a single herbicide. Key strategies include:

Cultural practices: crop rotation, cover crops, competitive varieties and timely planting to reduce weed pressure.
Mechanical control: targeted tillage, mowing and hand removal where practical.
Chemical strategies: rotate herbicide modes of action, use tank mixes appropriately, and apply correct rates and timing.
Monitoring and prevention: regular field scouting, early detection, sanitation of equipment to prevent spread, and managing weed seedbanks.

Adopting a diversified approach helps protect the efficacy of existing herbicides and reduces long‑term management costs. Producers and landowners with persistent weed problems are encouraged to consult local extension resources or K‑State guidance for region‑specific recommendations.