Can new herbicide discovery allow weed management to outpace resistance evolution?

Abstract

While herbicides are the most effective and widely adopted weed management approach, the evolution of multiple herbicide resistance in damaging weed species threatens the yield and profitability of many crops. Weeds accumulate multiple resistance mechanisms through sequential selection and/or gene flow, with long-range and international transport of herbicide-resistant weeds proving to be a serious issue. Metabolic resistance mechanisms can confer resistance across multiple sites of action and even to herbicides not yet discovered. When a new site of action herbicide is introduced to control a key driver weed, it likely will be one of very few effective available herbicide options for that weed in a specific crop due to the continuous use of herbicides over the years and the resulting accumulation of resistance mechanisms, placing it at even higher risk to be rapidly lost to resistance due to the high selection pressure it will experience. The number of available, effective herbicides for certain driver weeds is decreasing over time because the rate of resistance evolution is faster than the rate of new herbicide discovery. Effective monitoring for species movement and diagnostics for resistance should be deployed to rapidly identify emerging resistance to any new site of action. While innovation in herbicide discovery is urgently needed to combat the pressing issue of resistance in weeds, the rate of selection for herbicide resistance in weeds must be slowed through changes in the patterns of how herbicides are used.

The potential future roles of natural compounds and microbial bioherbicides in weed management in crops

“…This enzyme target is not used by any commercial herbicide. These are examples of potential herbicides with new modes of action that would be very useful in managing evolution of herbicide resistance, even though new modes of action alone are not a panacea for this problem (Gaines et al, 2021).…”

The search for new herbicide mechanisms of action: Is there a ‘holy grail’?

“…3,18 There are some caveats regarding the value of herbicides with new MOAs. 19 A herbicide with a new MOA is not necessarily a panacea to the evolved resistance problem. A large fraction of evolved resistance to herbicides is due to nontarget site resistance (NTSR) mechanisms, such as enhanced metabolic degradation, reduced uptake and/or translocation, and/or sequestration of the herbicide away from its molecular target (e.g.…”

“…There are some caveats regarding the value of herbicides with new MOAs 19 . A herbicide with a new MOA is not necessarily a panacea to the evolved resistance problem.…”

Hierarchical cluster analysis of herbicide modes of action reveals distinct classes of multiple resistance in weeds

“…1,2 Accordingly, over the last six decades, the number of herbicide-resistant weed species has grown dramatically to the point that currently there are >260 weed species known to have evolved resistance to one or more of 167 herbicides belonging to over 20 different MoAs. [3][4][5][6] This progressive increase in resistant weed species has occurred despite the ongoing implementation of herbicide resistance management strategies since the 1990s that have encouraged an integrated approach, consisting of crop and herbicide rotation with cultural and mechanical weed control. 3,7,8 The use of herbicide rotations or mixtures within an integrated approach, while potentially resulting in lower levels of target-site resistance, 3,8 also runs the risk of promoting nontarget-site resistance.…”

“…Herbicides are the primary tool for weed management in agricultural settings worldwide yet the repeated use of herbicides with the same mode of action (MoA) has resulted in the widespread evolution of resistance 1,2 . Accordingly, over the last six decades, the number of herbicide‐resistant weed species has grown dramatically to the point that currently there are >260 weed species known to have evolved resistance to one or more of 167 herbicides belonging to over 20 different MoAs 3–6 . This progressive increase in resistant weed species has occurred despite the ongoing implementation of herbicide resistance management strategies since the 1990s that have encouraged an integrated approach, consisting of crop and herbicide rotation with cultural and mechanical weed control 3,7,8 …”