Controlling Kochia (Kochia scoparia) in Soybean (Glycine max) with Postemergence Herbicides

Abstract

POST herbicides were applied at four soybean growth stages to evaluate their effect on triazine-resistant (TR) kochia in 1991, 1992, and 1993. Applying imazethapyr at 70 g ai/ha or bentazon plus imazethapyr at 1,120 plus 70 g ai/ha controlled 75 to 100% of 1- to 13-cm-tall TR kochia consistently across growth stages and years. Acifluorfen at 560 g ai/ha, chlorimuron at 13 g ai/ha, or chlorimuron plus thifensulfuron at 4 plus 4 g ai/ha controlled 68 to 96% of 1- to 2-cm-tall TR kochia at soybean growth stage VC to V1, and control was inconsistent at later growth stages. In most instances, soybean seed yield was greater with herbicides applied at the V1 or V2 growth stage of soybean compared with the V4 and V5 growth stage because of better weed control. No wheat yield reduction occurred because of herbicide carryover in 1992 and 1994. However, in 1993, imazethapyr and bentazon plus imazethapyr treatments applied in 1992 caused 22% injury and reduced winter wheat yield 10% when wheat was planted after soybean harvest.