Evaluation of Very-Long-Chain Fatty Acid-Inhibiting Herbicides in Arkansas Rice Production

Because of the evolution of herbicide-resistant weeds, such as barnyardgrass and red rice in rice, there is a need for alternative herbicide sites of action. Very-long-chain fatty acid (VLCFA)-inhibiting herbicides are not labeled for use in U.S. rice production; however, this site of action (SOA) has been used with success in Asian rice. The VLCFA-inhibiting herbicides pethoxamid, pyroxasulfone, acetochlor, and S-metolachlor were evaluated for rice tolerance and control of commonly problematic weeds in Arkansas rice at various rates and application timings. Pyroxasulfone and S-metolachlor were deemed unfit for use in rice production because of negative effects on rice visual injury, rough rice yield, height, shoot density, and heading. Pethoxamid and acetochlor were used with little detriment to the rice crop when applied no earlier than the 1-lf growth stage. Along with minimal rice injury, pethoxamid controlled barnyardgrass all season when used in a program with other common rice herbicides such as clomazone, imazethapyr, or quinclorac. Considering the minimal injury observed, pethoxamid and acetochlor should be considered for integration into U.S. rice production to represent a unique herbicide SOA to use in rotation, sequential application, or tank mixtures with other rice herbicides. Nomenclature: Acetochlor; pethoxamid; pyroxasulfone; S-metolachlor; barnyardgrass, Echinochloa crus-galli (L.) Beauv.; red rice, Oryza sativa var. sylvatica L.; rice, Oryza sativa L. Key words: weed control, herbicide-resistant weeds, herbicide sites of action