Oxyfluorfen use in Combination with Clomazone or Quinclorac

Abstract

Oxyfluorfen, a Herbicide Resistance Action Committee (HRAC)/Weed Science Society of America (WSSA) Group 14 herbicide that inhibits protoporphyrinogen IX oxidase, has shown significant potential in controlling barnyardgrass. Despite its current lack of labeling for use in midsouthern U.S. rice due to the potential for crop injury, the introduction of a trait in rice that confers resistance to oxyfluorfen could provide producers with an effective alternative site of action for weed control. Field experiments were conducted during the 2021 and 2022 growing seasons near Stuttgart, AR, and near Lonoke, AR, to determine the optimum rates of clomazone (280 or 336 g ha^-1) and oxyfluorfen (673 or 840 g ha^-1) to use in sequential preemergence (PRE) and postemergence (POST) applications on a silt loam soil and to assess the efficacy of oxyfluorfen when combined with clomazone and quinclorac PRE, followed by oxyfluorfen POST. No differences in barnyardgrass control were observed among treatments 14 days after emergence (DAE) in three site years, as all control was ≥90%. By 35 days after the postemergence application (DAPOST), all barnyardgrass control was ≥94% for herbicide treatments in all site years. All herbicide treatments resulted in lower barnyardgrass seed production than the nontreated in 2021. Contrasts revealed that oxyfluorfen applied PRE on a silt loam soil resulting in barnyardgrass control similar to clomazone or quinclorac alone at 14 DAE. Although oxyfluorfen combined with clomazone or quinclorac did not increase barnyardgrass control, an additional site of action for control of this weed could help reduce the evolution of resistance. Mixing oxyfluorfen with clomazone in a dry-seeded rice production system in the midsouthern U.S. would effectively control barnyardgrass and reduce the risk for resistance to both herbicides, further highlighting the potential of oxyfluorfen in rice production.