Identification of two Eleusine indica (goosegrass) biotypes of cool‐season turfgrass resistant to dithiopyr

BACKGROUND: Turfgrass managers reported poor Eleusine indica control following applications of the mitosis‐inhibiting herbicide dithiopyr in cool‐season turfgrass. Field, glasshouse, and laboratory experiments were conducted to understand the response of these biotypes to dithiopyr and prodiamine. RESULTS: In field experiments at two locations with putative dithiopyr‐resistant E. indica, preemergence applications of dithiopyr provided no E. indica control. Single applications of the protoporphyrinogen oxidase (PPO)‐inhibitor, oxadiazon, provided > 85% control at these locations. When subjected to agar‐based bioassays, root growth of putative resistant biotypes planted with 0.01 mmol L(−1) dithiopyr was slightly reduced (< 25%) whereas roots were completely inhibited in the susceptible biotype. Glasshouse whole plant rate‐response experiments found that the cytochrome P450 inhibitor, piperonyl butoxide (PBO), did not increase the sensitivity of these putative resistant biotypes to dithiopyr. Sequencing of α‐tubulin 1 (TUA1) revealed a Leu‐136‐Phe substitution in both dithiopyr‐resistant populations. CONCLUSION: Eleusine indica biotypes with resistance to dithiopyr are present in cool‐season turfgrass systems in the United States. Resistance is possibly related to a single nucleotide polymorphism (SNP) of an α‐tubulin gene. If turfgrass managers suspect resistance to dithiopyr, oxadiazon can still be an effective alternative for preemergence control. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.