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.

Experiments were conducted to determine adaptation characteristics to reduced irradiance of velvetleaf, common lambsquarters, eastern black nightshade, tumble pigweed, and soybean. Plants were grown to the 5- to 8-leaf stage in the greenhouse at ambient radiation (850 μE·m–2·s–1), and 26 and 13% of ambient radiation. Tumble pigweed, a C4 plant, had the highest light-saturated photosynthetic rates at all growth irradiances, while common lambsquarters had the highest rates of the four C3 species. All species adjusted to reduced irradiance by decreasing light-saturated photosynthesis, leaf respiration rates, root:shoot ratios, and leaf densities, while increasing leaf area ratios (LAR)3. As growth irradiance was reduced, support tissues (roots, stems, and petioles):leaf ratios did not change for common lambsquarters or velvetleaf, increased for soybean, and decreased for eastern black nightshade and tumble pigweed, indicating superior adaptation of the latter two species for efficient light harvesting at reduced growth irradiances. Of these five species, eastern black nightshade had the lowest respiration rate, the highest LAR, and the lowest support:leaf ratio for optimum adaptation to shaded environments.