Herbicides represent about 60% of the pesticides used worldwide. Bioherbicides are a growing portion of the herbicides used, but the several hundred commercial synthetic herbicides represent most of the herbicide market. Since their introduction about 70 years ago, weed management has been dominated by synthetic herbicides because of their efficiency and economic benefits to farmers. These herbicides have only about 20 modes of action, and resistance has evolved to most of them. New modes of action are needed for resistance management, but only a single new herbicide mode of action has been introduced in the last 30 years. Crops made resistant to the nonselective herbicide glyphosate through transgene technology have helped to make glyphosate the most used herbicide worldwide, but evolution of glyphosate‐resistant weeds is reducing reliance on glyphosate. New technologies, such as precision agriculture, will reduce herbicide use in the future.

Key Concepts

  • Herbicides are the principal means of weed management worldwide.
  • Most herbicides act by inhibiting the function of a single protein target (the mode of action).
  • Weeds have evolved resistance to most herbicide classes.
  • Crops made resistant to the herbicide glyphosate have played a dominant role in transgenic crops and in weed management.
  • Herbicides with new modes of action are badly needed for herbicide resistance management.

Keywords: bioherbicide; glyphosate; herbicide; herbicide‐resistant crop; mode of action; proherbicide; herbicide resistance

Figure 1. Amounts (weight) and sales (monetary value) of pesticide types of the top 30 pesticides worldwide in 2015. Reproduced with permission from Casida and Bryant 2017. © Royal Society of Chemistry.
Figure 2. Amounts (weight) and sales (monetary value) of herbicides types of the top 30 herbicides worldwide in 2015. Reproduced with permission from Casida and Bryant 2017. © Royal Society of Chemistry.
Figure 3. Accumulation of number of modes of herbicide action discovered from 1930 to 2018. Regression line highlights the steady discovery of approximately 1 unique MOA every two years from 1952 to 1984. This was followed by a 30‐year hiatus. A new mode of action was introduced in 2018 (Campe et al., ). Duke, https://onlinelibrary.wiley.com/doi/abs/10.1002/ps.2333.
Figure 4. Chronological increase in unique (species and MOA) cases of evolved herbicide‐resistant weeds worldwide. Regression line highlights the steady emergence of approximately 13 to 14 unique cases of evolved herbicide resistance from 1986 to the present day. Heap, https://onlinelibrary.wiley.com/doi/abs/10.1002/ps.4760.


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Further Reading

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Fedtke K and Duke SO (2005) Herbicides. In: Hock B and Elstner EF (eds) Plant Toxicology, pp. 247–330. New York: Marcel Dekker.

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Plimmer JR, Gammon DW and Ragsdale NN (eds) (2003) Encyclopedia of Agrochemicals, vol. 1–3. Hoboken, NJ: John Wiley & Sons, Inc.

Rao VS (2014) Transgenic Herbicide Resistance in Plants, p. 480. Boca Raton, FL: CRC Press.

Roe RM, Burton JD and Kuhr RJ (eds) (1997) Herbicide Activity: Toxicology, Biochemistry and Molecular Biology, p. 205. Amsterdam, The Netherlands: IOS Press.

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Duke, Stephen O, and Dayan, Franck E(Oct 2018) Herbicides. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0025264]