Control of Glyphosate-Resistant Marestail in Identity-Preserved or Glyphosate-Resistant and Glyphosate/Dicamba-Resistant Soybean with Preplant Herbicides

Two studies, each consisting of six field experiments were conducted in growers’ fields in 2018 and 2019 to determine the optimal herbicide tankmixes, applied preplant (PP) for the control of glyphosate-resistant (GR) marestail in 1) identity-preserved and glyphosate-resistant soybean (Study 1) and, 2) glyphosate/dicamba-resistant soybean (Study 2). There was no significant injury in soybean with the PP herbicides evaluated in both studies. In Study 1, at 8 weeks after treatment (WAA), glyphosate + saflufenacil, glyphosate + 2,4-D ester, glyphosate + pyraflufen/2,4-D, glyphosate +, 4-D choline or glyphosate + halauxifen-methyl, applied PP, controlled GR marestail 93%, 58%, 60%, 67% and 71%, respectively. The addition of metribuzin to the tankmixes of glyphosate + saflufenacil, 2,4-D ester and pyraflufen/2,4-D increased the control to 98%, 91% and 95%, respectively. The addition of metribuzin + chlorimuron-ethyl to 2,4-D choline/glyphosate and glyphosate + halauxifen-methyl increased the control to 94% and 93%, respectively. In Study 2, at 8 WAA, glyphosate/dicamba, applied PP, controlled GR marestail 89% in glyphosate/dicamba-resistant soybean. The addition of metribuzin or saflufenacil to glyphosate/dicamba controlled GR marestail 86% and 97%, respectively. At 8 WAA, S-metolachlor/dicamba controlled GR marestail 83%. The addition of metribuzin or saflufenacil to the above premix controlled GR marestail 87% and 97%, respectively. Density and biomass reductions were similar to visible control. GR marestail interference reduced soybean yield 60% and 53% in Study 1 and 2, respectively. Reduced GR marestail interference with all the herbicide treatments evaluated in both studies resulted in soybean yield that was similar to the weed-free control.