In input-intensive cropping systems around the world, farmers rarely proactively manage weeds to prevent or delay the selection for herbicide resistance. Farmers usually increase the adoption of integrated weed management practices only after herbicide resistance has evolved, although herbicides continue to be the dominant method of weed control. Intergroup herbicide resistance in various weed species has been the main impetus for changes in management practices and adoption of cropping systems that reduce selection for resistance. The effectiveness and adoption of herbicide and nonherbicide tactics and practices for the proactive and reactive management of herbicide-resistant (HR) weeds are reviewed. Herbicide tactics include sequences and rotations, mixtures, application rates, site-specific application, and use of HR crops. Nonherbicide weed-management practices or nonselective herbicides applied preplant or in crop, integrated with less-frequent selective herbicide use in diversified cropping systems, have mitigated the evolution, spread, and economic impact of HR weeds.

Additional index words: Herbicide resistance, integrated weed management.

Abbreviations: ACCase, acetyl-CoA carboxylase; ALS, acetolactate synthase; APP, aryloxyphenoxypropionate; CHD, cyclohexanedione; DSS, decision-support system; EPSPS, enolpyruvylshikimate-3-phosphate synthase; HR, herbicide resistant; HS, herbicide susceptible; IWM, integrated weed management.