Field studies were conducted from 1986 through 1989 to determine the feasibility of using clomazone in a winter wheat-corn-fallow rotation. Clomazone at 1.1 kg ai/ha did not control emerged downy brome in autumn nor did it control redroot pigweed and tumble pigweed that emerged after a spring application of paraquat at 0.6 kg ai/ha. However, clomazone plus atrazine at 0.6 plus 2.2 kg ai/ha provided weed control in winter wheat stubble from October to corn harvest 12 mo later. Corn yields from this treatment were equal to or greater than the conventional practice of applying atrazine plus glyphosate at 2.2 plus 0.4 kg ae/ha in the fall followed by a spring application of metolachlor plus dicamba at 2.8 ai plus 0.3 kg ae/ha. When kochia densities were high, clomazone plus atrazine controlled triazine-resistant kochia better than metolachlor plus dicamba. Atrazine at 2.2 kg/ha applied in autumn followed by clomazone at 0.8 kg/ha in April generally caused more corn injury than when the same rate of clomazone was applied in autumn with the atrazine. The percent of bleached corn plants varied with planter, year, time of application, and rate of clomazone applied. The optimum time to apply clomazone at 0.6 kg/ha was in autumn with atrazine. This treatment caused some corn bleaching but produced the highest corn yield over 3 yr. In a dry autumn and spring, less clomazone injury occurred with a planter equipped with row cleaners than those without. The injury pattern associated with planters was inconsistent when precipitation was average and no injury occurred in a wet autumn and spring.

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.