A five-year examination into the occurrence of herbicide-resistant barnyardgrass populations in paddy from Jiangsu Province, China.

To assess resistance situation and evolutionary risks, 510 Echinochloa populations from 13 rice-growing regions in Jiangsu Province (2018-2022) were tested against seven herbicides (penoxsulam, quinclorac, cyhalofop-butyl, bispyribac-sodium, pretilachlor, metamifop, and florpyrauxifen-benzyl), with cross- and multiple-resistance patterns analyzed. Penoxsulam resistance increased ninefold over five years, while quinclorac resistance consistently exceeded 40% annually for four years. Cyhalofop-butyl and bispyribac-sodium resistance frequencies also rose annually, with the strongest resistance to penoxsulam and bispyribac-sodium observed in southern Jiangsu, particularly in Suzhou, Wuxi, Changzhou, and Zhenjiang. In northern Jiangsu, Huaian showed the highest resistance to multiple herbicides, while quinclorac resistance was widespread across all regions. Pretilachlor and metamifop resistance remained low, with only sporadic outbreaks, indicating that they continued to be used. However, prolonged use of single-site herbicides, particularly ALS inhibitors and ACCase inhibitors, has led to cross-resistance evolution. Multiple-resistance analysis indicated that quinclorac, penoxsulam, and cyhalofop-butyl should not be used in binary or ternary mixtures to control resistant Echinochloa. Notably, 14 populations exhibited florpyrauxifen-benzyl resistance, with 13 also showing quinclorac resistance, suggesting a potential link between prior quinclorac resistance and florpyrauxifen-benzyl resistance evolution, which warrants further investigation. This study clarifies herbicide resistance patterns in Echinochloa in Jiangsu Province, offering critical insights for resistance management strategies.