Baseline sensitivity of Echinochloa crus-galli (L.) P.Beauv. to tripyrasulfone, a new HPPD-inhibiting herbicide, in China

Tripyrasulfone is an 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicide applied postemergence (POST) to control Echinochloa crus-galli (L.) P.Beauv. and other annual weeds in directly seeded and transplanted paddy fields in China. In this study, the baseline sensitivity to tripyrasulfone of E. crus-galli in paddy fields in China was established using dose-response assays between June and September 2020. The results showed that the sensitivity to tripyrasulfone varied among 58 populations collected from paddy fields in China. The tripyrasulfone dose causing a 50% growth reduction (GR50) in the 58 field populations ranged from 1.95 to 46.47 g a.i. ha-1, and no populations showed resistance to tripyrasulfone. At the same time, the GR50 values were not normally distributed (P < 0.0001) but distributed as a unimodal curve, and the baseline sensitivity (GR50b) to tripyrasulfone for E. crus-galli in paddy fields in China was 18.12 g a.i. ha-1. The SI50 value (the ratio between the GR50 values of the least and most sensitive populations) showed 23.8-fold variability in tripyrasulfone sensitivity among the 58 E. crus-galli field populations, while the variability declined from 23.8-fold to 2.6-fold when the SI50b value (the ratio between the GR50 values of the least sensitive population and the GR50b) was used. This study confirmed the effectiveness of tripyrasulfone against E. crus-galli in paddy fields in China and provided a reference for detecting time-dependent shifts in the tripyrasulfone sensitivity of E. crus-galli field populations.