Herbicide Strategies for Managing Kochia (Kochia scoparia) Resistant to ALS-Inhibiting Herbicides in Wheat (Triticum aestivum) and Soybean (Glycine max)1

Kochia (Kochia scoparia) control dropped from about 90% to less than 20% after three consecutive annual applications of acetolactate synthase (ALS)-inhibiting herbicides in several northeastern South Dakota fields. Field experiments were conducted to evaluate control of kochia resistant to ALS-inhibiting herbicides using combinations of herbicides applied postemergence (POST) in wheat (Triticum aestivum) and using herbicides applied preemergence (PRE), POST, and PRE plus POST in soybean (Glycine max). Thifensulfuron plus tribenuron did not control kochia in wheat (> 600 kochia plants/m2 at harvest) and wheat yield was similar to yield of the untreated control. Dicamba plus 2,4-D (in 1996) and bromoxynil plus MCPA (in 1996 and 1997) controlled kochia and increased yields by 15% or more. Kochia was sparse (less than 1 plant/m2) in soybean plots, but grass weeds were prevalent. PRE plus POST or POST herbicide combinations that included ALS-inhibiting herbicides controlled grasses, and soybean yield...