Herbicide Resistance in Weeds and Crops: Challenges and Opportunities

Abstract

Since the discovery of triazine resistance in broadleaf weed populations in the late 1960s, herbicide-resistant (HR) weeds have now infested crop and non-crop areas worldwide for almost half a century. However, it was not until the mid-1990s with the advent of HR crops that use of a single herbicide site of action, glyphosate, was repeatedly applied over millions of hectares of glyphosate-resistant crops annually. Concomitantly, intergroup (across site of action)-HR weed biotypes were being reported worldwide at a rate of two per year, including those resistant to glyphosate. The promise of reduced herbicide use with the introduction of HR crops was realized, but did not last; herbicide use inevitably increased to manage glyphosate- and intergroup-HR weeds in HR maize, soybean, and cotton. The pending introduction of new multiple- or stacked-trait HR crops is an opportunity to get it right this time, through grower implementation of more diversified cropping systems and weed management practices. We already have the knowledge and information of best management practices to proactively and reactively manage HR weeds. Growers have a narrow window of opportunity to adopt these practices. They can expect few herbicides with new sites of action to be commercialized in the short to medium term. Continued research and development of non-herbicidal technology to reduce the selection pressure of the remaining effective arsenal of herbicides should aid growers in managing their HR weeds.