Assessment of Florpyrauxifen-Benzyl Sensitivity in Echinochloa crus-galli and E. crus-galli var. mitis: A Case Study with 228 Populations in Eastern China

Echinochloa crus-galli and E. crus-galli var. mitis are two of the most troublesome rice weeds. Florpyrauxifen-benzyl is one of the most important post-emergence rice herbicides that has been pervasively applied in many countries since 2018. We collected 70 E. crus-galli and 158 E. crus-galli var. mitis populations from rice fields in eastern China in 2022 and tested their sensitivities to florpyrauxifen-benzyl through whole-plant bioassays. A total of 21 days after treatment with florpyrauxifen-benzyl label dose (36 g ai ha−1), 71.4% of E. crus-galli and 70.9% of E. crus-galli var. mitis populations were completely controlled. The GR50 doses (doses causing 50% fresh weight reductions in aboveground parts) of florpyrauxifen-benzyl applied to E. crus-galli populations ranged from 1.4 to 36.9 g ai ha−1, with a baseline sensitivity dose of 4.9 g ai ha−1; those for E. crus-galli var. mitis populations ranged from 1.3 to 97.6 g ai ha−1, with a baseline sensitivity dose of 5.0 g ai ha−1. No significant differences between E. crus-galli and E. crus-galli var. mitis were found in GR50 values. Among 70 E. crus-galli populations, 61.4%, 35.7%, and 2.9% showed no, low, and moderate resistance to florpyrauxifen-benzyl, while among 158 E. crus-galli var. mitis populations, 54.4%, 36.1%, 1.9%, and 1.9% showed no, low, moderate, and high resistance to florpyrauxifen-benzyl, respectively. Moreover, the frequency of florpyrauxifen-benzyl-resistant populations of E. crus-galli var. mitis tended to be higher in southwestern areas.