Oxyfluorfen is a herbicide that inhibits protoporphyrinogen IX oxidase and has shown significant potential in its ability to control barnyardgrass. Oxyfluorfen is categorized as a Group 14 herbicide by the Herbicide Resistance Action Committee (HRAC)/Weed Science Society of America (WSSA). Despite its current lack of labeling for use on rice in the midsouthern United States due to its potential to cause 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 applied PRE, followed by oxyfluorfen applied POST. No differences in barnyardgrass control were observed among treatments 14 d after emergence in 3 site years, as all control was ≥90%. By 35 d after the POST application, barnyardgrass control was ≥94% for all herbicide treatments in all site years. All herbicide treatments resulted in lower barnyardgrass seed production than a nontreated control in 2021. Contrasts revealed that oxyfluorfen applied PRE on a silt loam soil resulted in barnyardgrass control that was similar to that of clomazone or quinclorac applied alone at 14 d after emergence. 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 mid-southern United States would effectively control barnyardgrass and reduce the risk for resistance to both herbicides, further highlighting the potential of oxyfluorfen in rice production.

Nomenclature: Clomazone; oxyfluorfen; quinclorac; barnyardgrass, Echinochloa crus-galli (L.) P. Beauv.; rice, Oryza sativa L.