Best Management Practices to Prevent, Delay, or Manage Herbicide Resistance

Effectively managing weeds to prevent losses in crop yield and quality, degradation of natural landscapes, and impairment of the utility of terrestrial and aquatic landscapes has, in many ways, been greatly simplified by the development of herbicides. However, repeated use of herbicides with similar mechanisms of action (MOAs) imposes tremendous selection pressure for the evolution of herbicide-resistant plants. Currently more than 200 plant species have been confirmed resistant to herbicides worldwide. Preventing or delaying the evolution of herbicide resistance, or managing herbicide resistance when it has already evolved, fundamentally depends on eliminating weed seed in the soil seedbank. Accomplishing this requires a multifaceted approach focused on long-term weed management strategies that involve cultural, mechanical, and biological methods as well as herbicides. The following Best Management Practices (BMPs) are essential elements of these strategies: Understand the biology of the weeds present; Use a diversified approach toward weed management focused on preventing weed seed production and reducing the number of weed seeds in the soil seedbank; Plant into weed-free fields and then keep fields as weed free as possible; Plant weed-free crop seed; Scout fields routinely; Use multiple herbicide MOAs that are effective against the most troublesome weeds or those most prone to herbicide resistance; Apply the labeled herbicide rate at recommended weed sizes; Emphasize cultural practices that suppress weeds by using crop competitiveness; Use mechanical and biological management practices where appropriate; Prevent field-to-field and within-field movement of weed seed or vegetative propagules; Manage weed seed at harvest and after harvest to prevent buildup of the weed seedbank; and Prevent an influx of weeds into the field by managing field borders.