Effectiveness of Preemergence- and Postemergence-Applied Oxyfluorfen in Rice Compared to Current Standards

Abstract Control of barnyardgrass is becoming increasingly difficult as plants evolve resistance to herbicides. ROXY oxyfluorfen-resistant rice (ROXY ® Rice Production System) has been developed to allow for an alternative mode of action to control barnyardgrass and other weeds. In 2021 and 2022, field trials were conducted at the Pine Tree Research Station near Colt, AR, the Northeast Research and Extension Center in Keiser, AR, and the University of Arkansas Pine Bluff Small Farm Research Center near Lonoke, AR to determine the level of weed control and crop tolerance following oxyfluorfen applied preemergence or postemergence relative to herbicides currently labeled for use in rice. When applied post-plant preemergence on silt loam soil, oxyfluorfen alone at 1,120 and 1,680 g ai ha -1 resulted in barnyardgrass control comparable to clomazone alone at 336 g ha -1 . Still, injury to rice was often greater than with clomazone, ranging from 20% to 45%. On clay soil, oxyfluorfen at 1,680 g ha -1 resulted in barnyardgrass control comparable to clomazone alone in both site-years at three weeks after emergence but caused up to 18% injury to rice. When oxyfluorfen was applied at 560 to 1,680 g ha -1 at the 2-leaf rice growth stage, barnyardgrass control was ≥85% in three of four site-years one week after treatment. However, injury to rice ranged from 38% to 73% for the rates evaluated. Propanil caused the greatest injury by a herbicide currently labeled for use in rice at 34%. Oxyfluorfen should be used as a post-plant preemergence herbicide rather than a postemergence herbicide due to the injury observed after a postemergence application. The data indicates that if used as a preemergence herbicide, oxyfluorfen should be applied at 560 g ha -1 to reduce the injury observed on silt loam and clay soils.