Activity of Isoxaflutole plus Metribuzin Tankmixes in Isoxaflutole-Resistant Soybean

Abstract

Isoxaflutole-resistant soybean is currently in development for commercialization in North America. Proposals to use isoxaflutole + metribuzin as the main herbicide tank-mixture raise concerns as there is limited grass control with these herbicides. Strategies are needed to improve grass control with isoxaflutole + metribuzin. Nine experiments were conducted over a two-year period (2017, 2018) to determine the efficacy of isoxaflutole + metribuzin (52.5 + 210 g a∙i∙ha−1) applied alone and co-applied with pendimethalin, dimethenamid-P, pethoxamid, pyroxasulfone or S-metolachlor applied preemergence (PRE). Comparisons were made with isoxaflutole + metribuzin at a low rate (52.5 + 210 g a∙i∙ha−1), medium rate (79 + 315 g a∙i∙ha−1) and a high rate (105 + 420 g a∙i∙ha−1). Eight weed species were evaluated including common lambsquarters, green and redroot pigweed, common ragweed, velvetleaf, green and giant foxtail, yellow foxtail, barnyardgrass and witchgrass. All herbicides were affected by amount of rainfall following application; less rainfall resulted in reduced weed control. The addition of pendimethalin, dimethenamid-P, pethoxamid, pyroxasulfone or S-metolachlor to the low rate ofisoxaflutole + metribuzin provided equivalent control of all weed species evaluated compared toisoxaflutole + metribuzin at the low, medium, or high rate.