By Tripp Rogers and Travis Gannon

Herbicide-resistant weeds are a leading problem in the turfgrass industry. Herbicide-resistant weed biotypes within a population may compromise the functionality and aesthetic of turfgrass systems while simultaneously imparting social and economic pressure on professional turfgrass managers.

What is herbicide resistance? Herbicide-resistant weeds are not a new problem in turfgrass systems (or any system). In fact, herbicide resistance was documented as early as 1970. Herbicide resistance is a selection process that develops through the repeated use of the same herbicide or herbicides with the same mechanism of action (MOA). Typically, herbicide resistance traits are present within a population at very low levels (~< 0.001%) (Petelewicz et al. 2023) and the continuous application of the same herbicide (or herbicide with same MOA) over time removes susceptible plants while allowing resistant individuals to survive, grow, reproduce, and proliferate.

Herbicide resistance can be characterized by cross- and multiple-resistance. Cross-resistance is defined as a population that is resistant to other herbicides or chemical families within the same MOA. For example, a population may be resistant to imidazolinones and sulfonylureas, which are both acetolactate synthase (ALS)-inhibiting [Herbicide Resistance Action Committee (HRAC) Group 2] herbicides. Multiple-resistance refers to weed populations that are resistant to herbicides with different MOAs. An example would be a population that is resistant to both ALS-inhibiting (HRAC Group 2) herbicides and photosystem (PS) II-inhibiting (HRAC Group 5) herbicides such as atrazine or simazine. Although cross-resistance is more common; multiple-resistant weeds are often more problematic, as control options are inherently more limited. The most effective method to mitigate cross-resistance is to rotate MOAs. However, managing multiple-resistant weed populations may require implementing other means of weed control outside of chemical control such as mechanical (i.e., fraise mowing) or cultural control practices.

Read the full article in the Spring 2025 issue of Arkansas Turfgrass – https://theturfzone.com/arkansasturf/?ascat=77&sub=issue&issue_id=9392&rti=true&rel=2