LAUSR

BACKGROUND Turfgrass managers reported poor Eleusine indica control following applications of the mitosis-inhibiting herbicide dithiopyr in cool-season turfgrass. Field, greenhouse, 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 mM dithiopyr was slightly reduced (< 25%) whereas roots were completely inhibited in the susceptible biotype. Greenhouse 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 E. 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. This article is protected by copyright. All rights reserved.