Group 4 - Auxin Mimics Resistance
Auxin mimics (Group 4) are a class of herbicides that mimic the natural plant hormone auxin, which regulates plant growth. When applied in high concentrations, these synthetic compounds disrupt normal growth processes, leading to uncontrolled cell division, abnormal tissue development, and ultimately plant death—especially in broadleaf (dicot) weeds.
As of 2025, resistance to auxin mimics herbicides is intensifying globally, with new genetic mechanisms being identified—such as mutations in auxin signaling genes that disrupt herbicide action. Resistance is also spreading geographically, with cases emerging in new regions and involving multiple herbicide modes of action. Both target-site and non-target-site resistance mechanisms are contributing to this trend, prompting increased surveillance, diagnostic testing, and collaborative efforts to develop integrated weed management strategies.
Check the current status of herbicide resistance cases to Group 4 or auxin mimics herbicides:
https://weedscience.org/Pages/MOA.aspx
The Auxin Mimics Working Group is dedicated to safeguarding the long-term efficacy of auxin mimics herbicides by advancing global understanding and management of herbicide resistance. The team supports sustainable weed control strategies to combat auxin resistance and preserve the utility of this vital herbicide class. We also work closely with other working groups such as the Mode of Action Working Group to maintain the most accurate information about Group 4 herbicides in our HRAC MoA classification poster (https://hracglobal.com/hrac-global-herbicide-moa-classification-explorer)
Synthetic Auxin Resistance
Synthetic auxins were the first highly effective, and selective organic herbicides. They have been used for over 60 years and are still being used extensively worldwide.
Download Synthetic Auxin Resistance PDF
Corn Poppy
Corn poppy is the most important broadleaf weed of winter wheat in southern Europe. Synthetic auxins, particularly 2,4‐D, have been used to control corn poppy in winter wheat for over 60 years.
Kochia
Kochia is a widespread annual weed known for its adaptability. Evidence of triazine resistance was detected as early as 1976 and to the ALS herbicides in the 1980's.
Lambsquarters
Common lambsquarters is a rapidly growing summer annual weed found in many agricultural systems. Synthetic auxins have long been used for control of common lambsquarters throughout the world.
Tall Waterhemp
Waterhemp is a significant weed of corn and soybean production in the Midwest of the US. Waterhemp has evolved resistance to six herbicide mechanisms of action.
Wild Radish
Wild radish is the second most economically important weed of crops in Australia and a common weed of crops globally. It has evolved resistance to five mechanisms of action, the last being to synthetic auxins in 1999 in western Australia.
Wild Mustard
Wild mustard is a common and serious weed of cereal production throughout the world. Populations of synthetic auxin resistant wild mustard were first found in cereal production in Manitoba, Canada in 1990.