Clomazone and Oxyfluorfen Combinations in a Flooded Rice System

Abstract

Rice producers battle herbicide-resistant weeds worldwide while producing rice for ≥50% of the world’s population. Oxyfluorfen can provide rice producers with an alternative site of action for barnyardgrass control, as there are no documented cases of grass weeds being resistant to the herbicide in the midsouthern United States. Oxyfluorfen is anticipated to be labeled in the Roxy Rice Production System and may be sold as a clomazone:oxyfluorfen premixture; hence, experiments were conducted in 2021 and 2022 to evaluate preemergence-applied clomazone:oxyfluorfen ratios compared to clomazone alone on silt loam and clay soils. All ratios of the herbicides caused less than 7% injury to rice in two of four site-years on silt loam soils, whereas, in the two other site-years, the mixtures caused 10% to 40% rice injury at all observation timings. All combinations of the two herbicides provided at least 73% barnyardgrass control 5 weeks after rice emergence (WAE) in three of the four site-years on silt loam soils. In at least two of four site-years at 1 and 3 WAE, barnyardgrass control was improved when oxyfluorfen was added to clomazone compared to clomazone alone. On clay soil, barnyardgrass control in both site-years was ≥77% at 5 WAE for all clomazone and oxyfluorfen ratios. Injury to rice ranged from 13% to 30% for all treatments containing clomazone and oxyfluorfen in one of two site-years on clay soil at all observation timings. At 7 WAE, contrasts indicated that the 1:3 ratio of clomazone to oxyfluorfen provided greater barnyardgrass control than the 1:1.5 and 1:2 ratios in one of two site-years. Based on these findings, oxyfluorfen would improve the consistency of barnyardgrass control over clomazone alone in some instances. However, there is an increased risk of injury to rice with the addition of oxyfluorfen.