Herbicide-Resistant Weeds: Unanswered Questions and Effective Strategies

Thursday, May 25, 2023

Herbicide-resistant weeds pose a significant challenge for agronomic crop production, with the evolution of resistance mechanisms continuing to perplex scientists. While there are 520 cases of herbicide resistance globally, our understanding of how and why these mechanisms develop is progressing slowly.

This knowledge gap hampers the development of effective herbicide recommendations to manage resistance. Some recommendations, such as diversifying herbicide modes of action through rotations and tank-mixtures, have been promoted but lack comprehensive data on their landscape-level effectiveness.

A research project in Illinois explored the evolution of glyphosate-resistant waterhemp and found that simply rotating herbicide modes of action increased resistance frequency. On the other hand, using tank-mixtures with multiple modes of action greatly reduced the selection for resistance.

However, it is important to note that these findings focused on target site-based resistance mechanisms, and data on nontarget site-based mechanisms are limited. Research from Europe even suggested that herbicide mixtures may favor the evolution of generalized resistance mechanisms rather than specialized ones.

Understanding which herbicides remain effective against resistant weed populations remains challenging, and there is no foolproof way to determine efficacy. Adding soil-residual herbicides, layering residuals with postemergence applications, or tank-mixing multiple herbicides may seem like solutions, but their long-term impact on resistance evolution is uncertain.

To prevent weed seed production and the emergence of new resistance mechanisms, it is crucial to employ additional tactics alongside herbicide use. While herbicides remain valuable tools for preventing crop yield loss, a comprehensive approach that considers diverse strategies to ensure no weed seed production is necessary.

Emphasizing the prevention of seed production will be crucial in managing herbicide-resistant weeds effectively. By adopting a holistic approach and exploring alternative methods, farmers can mitigate the challenges posed by herbicide-resistant weeds and protect the long-term productivity of their crops.