Barnyardgrass (Echinochloa crus-galli) control and rice injury with labeled herbicides following exposure to sub-lethal concentrations of paraquat

Rice in Mississippi is often in early seedling growth stages when paraquat-based herbicide treatments are commonly applied to corn, cotton, and soybean; therefore, off-target movement onto adjacent rice fields may occur. After an off-target movement event has occurred, weed management in the rice crop is still necessary. Field studies were conducted from 2019 to 2021 in Stoneville, MS, to evaluate rice injury and barnyardgrass control with labeled herbicides after exposure to a sub-lethal paraquat concentration. Labeled herbicide treatments were recommended rates of imazethapyr, quinclorac, propanil, bispyribac-sodium, cyhalopfop, and florpyrauxifen-benzyl applied following rice exposure to a sub-lethal concentration of paraquat. Rice injury was detected 7 and 28 d after treatment (DAT) with injury ≥ 35 and 14%, respectively, following all labeled herbicides. Florpyrauxifen-benzyl and imazethapyr injured rice the greatest 28 DAT. Following paraquat exposure, barnyardgrass control was similar for all labeled herbicide treatments 7, 14, and 28 DAT except with florpyrauxifen-benzyl and no labeled herbicide (paraquat alone) 7 DAT. Across all evaluations, barnyardgrass control was at least 12% greater following paraquat exposure and labeled herbicide treatments than with no paraquat exposure. The current research demonstrates that labeled herbicides applied following exposure to a sub-lethal concentration of paraquat resulted in <36% injury and provided as great as 95% control of barnyardgrass, depending on the herbicide treatment. Therefore, the labeled herbicides choice following rice exposure to a sub-lethal concentration of paraquat should be based on weed spectrum.