As herbicide-resistant weeds have evolved over time, recommendations of strategies to mitigate this process have also evolved. In fact, some of the early discoveries of herbicide resistance misled the weed science community into making, in hindsight, naïve recommendations for resistance management. For example, previously it was believed that herbicide resistance was most commonly due to target-site mutations that conferred high magnitudes of resistance and were accompanied with significant fitness costs in the absence of the herbicide. Consequently, annual rotation of herbicides with different sites of action was a predominant recommendation. Today, it is recognized that herbicide resistance often is not accompanied with a substantial fitness cost and that resistance is increasingly due to multigenic, nontarget-site (NTS) mechanisms (such as increased herbicide metabolism). Because NTS resistance can confer unpredictable patterns of cross resistance, including to herbicides with different sites of action, simply rotating or mixing herbicides is not always effective to mitigate NTS resistance, and may actually enhance its evolution. A major driver for the evolution of herbicide-resistant weeds is not only over-reliance on herbicides for weed control, but also, oftentimes, over-reliance on a single herbicide in specific situations. For example, in the early 2000s, one herbicide—glyphosate—was used almost exclusively for weed control in U.S. soybean. Historically, herbicide-discovery efforts led rather consistently to new commercialized options, allowing farmers to rely on the most cost-effective herbicides available at the time with confidence that new products would be available should resistance evolution render current products ineffective. However, during the past few decades, the pace of new herbicides, particularly those with novel sites of action, entering the market has slowed dramatically. This fact, together with increasing cases of NTS resistance and multiple resistance in weed populations, paints a bleak future for chemical weed management. Current recommendations for mitigating herbicide resistance still include rotating and mixing herbicides but increasingly focus on including non-chemical strategies and reducing the soil seed bank. Convincing farmers to adopt such strategies remains the greatest challenge.

Strategies to mitigate herbicide resistance: Where we have been and where we are going

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.