Metamifop resistance of Echinochloa glabrescens populations collected from rice fields in Jiangsu Province, China

Echinochloa glabrescens is one of the most problematic rice weeds in Jiangsu Province, China. metamifop is a crucial post-emergence rice herbicide used to control Echinochloa weeds. In this study, we evaluated the resistance levels of 114 E. glabrescens populations collected from rice fields across Jiangsu in 2022 against metamifop. The results showed that at 28 days after treatment of seedlings at the 3-5 leaf stage, the recommended dose of metamifop (120 g a.i./hm²) reduced the fresh weight of these populations by 21.7%-100%, with an average of 91.8%. The dose of metamifop causing a 50% reduction in fresh weight (GR₅₀) ranged from 4.4-268.3 g a.i./hm². The baseline sensitivity of metamifop to E. glabrescens was determined to be 37.8 g a.i./hm². Among the tested populations, 7.0%, 45.6%, 27.2%, and 20.2% were sensitive, low resistant, moderate resistant, and high resistant to metamifop, respectively. Notably, populations collected from Nantong and Zhenjiang cities exhibited significantly higher resistance levels to metamifop than those collected from the other 11 cities. These findings suggested that while metamifop is an important rice herbicide for managing Echinochloa weeds, it faces severe challenges due to resistant populations, particularly in direct-seeded rice fields. Our results provide a theoretical basis for predicting the market lifespan of metamifop as a rice herbicide and for adjusting its promotion strategy at a regional scale.