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Department of Agronomy

Herbicide Resistance

Herbicide-Resistant Weeds

A herbicide-resistant biotype of a weed species is a population of plants that is not controlled by the normal application rate of a herbicide. It is not controlled by a given herbicide because it has a genetic change that prevents the herbicide from working as it should. A herbicide-susceptible biotype of a weed species is a population of plants that is controlled by the normal application of a herbicide.

A number of weed species in Kansas’ crops have developed resistance to different herbicides, and some to multiple herbicides. To learn more about their biology and options for control, reference table below.

Weed Species

Kochia (Kochia scoparia)Marestail / Horseweed (Conyza canadensis)
Kochia (Kochia Scoparia)Marestail / Horseweed (Conyza Canadensis)
Mustard Species (Bushy Wallflower (Erysimum Repandum) and Flixweed (Descurainia Pinnata or Descurainia Sophia))Pigweed Species (Palmer Amaranth, Common Waterhemp, Redroot Pigweed)

Herbicide Modes of Action

Type of Herbicide Resistance / Mode of ActionWeed SpeciesYear Discovered
ALS-inhibitorsRussian Thistle1988
ALS-inhibitorsCommon Waterhemp1993
ALS-inhibitorsPalmer Amaranth1994
ALS-inhibitorsCommon Cocklebur1997
ALS-inhibitorsCommon Sunflower1997
ALS-inhibitorsJapanese Brome2007
TriazinesDowny Brome1977
TriazinesPalmer Amaranth1994
TriazinesRedroot Pigweed1996
TriazinesCommon Waterhemp1997
GlycinesCommon Waterhemp2006
GlycinesGiant Ragweed2006
GlycinesCommon Ragweed2006
PPO-inhibitorCommon Waterhemp2001
3-way multiple resistance
(triazine, ALS- and PPO-inhibitors)
Common Waterhemp2002