Effectiveness of 2,4-D/dicamba/dichlorprop-p premixture for controlling glyphosate-resistant kochia ( <i>Bassia scoparia</i> L.) in Central Great Plains

Abstract Widespread evolution of glyphosate resistance among kochia populations is a serious challenge for growers across the North American Great Plains. Dicamba has historically been used to control glyphosate-resistant (Gly-R) kochia. However, the increasing spread of dicamba-resistant kochia and current restrictions on dicamba use (low volatile formulations) warrant alternative herbicide options to control Gly-R kochia. In this context, field-based dose response experiments were conducted in fallow at Kansas State University Agricultural Research Center, Hays, KS, during 2021 and 2022 to determine and compare the effectiveness of 2,4-D, dicamba, and dichlorprop-p applied alone, and in a premixture of 2,4-D/dicamba/dichlorprop-p for controlling Gly-R kochia. Averaged across two years, results indicated that substantially lower doses of 2,4-D, dicamba, and dichlorprop-p were required in a premixture to achieve effective control of Gly-R kochia compared with their standalone applications. Specifically, the ED 90 values for Gly-R kochia control were reduced by 90-, 4-, and 6-times for 2,4-D, dicamba, and dichlorprop-p, respectively, when applied as a premixture. Similarly, achieving 90% biomass reduction required approximately 1021-, 3-, and 4-times lower doses of 2,4-D, dicamba, and dichlorprop-p, respectively, in the premixture than when applied alone. Altogether, these results demonstrated that the premixture of 2,4-D/dicamba/dichlorprop-p can be an effective alternative for managing Gly-R kochia in fallow. The reduced dose requirements in a premixture also suggested potential benefits for resistance management, cost efficiency, and environmental stewardship.