Herbicides

Abstract 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.