Field studies were conducted in 1991 and 1992 to evaluate the response of soybean and the subsequent rice crop to AC 263,222 applied alone and in tank mixtures with imazethapyr or imazaquin. In 1991, 18, 36, and 70 g ai/ha of AC 263,222 visibly stunted soybean 9, 19, and 35%, respectively. Adding imazethapyr at 36 g/ha or imazaquin at 70 g/ha to AC 263,222 in a tank mixture did not increase soybean response compared to AC 263,222 alone. Soybean yield was not reduced by any treatment. In 1992, 14 g/ha of AC 263,222 alone or in tank mixtures damaged soybean 38% or greater. In one study, rice was injured the year following application of AC 263,222 alone and in tank mixtures. Rice yield was reduced by 70 g/ha of AC 263,222 alone and by 36 g/ha of AC 263,222 when tank mixed with 36 g/ha of imazethapyr.

Field experiments were conducted in Louisiana over 2 yr to evaluate the influence of full-season interference from johnsongrass, common cocklebur, or hemp sesbania at densities of 2.5, 0.5, and 2.0 plants m–1of row, respectively, and simulated insect defoliation of soybean on weed and soybean growth. Defoliation at R2 (full bloom) and R5 (beginning seed development) soybean growth stages was accomplished by removal of zero, one, or two leaflets per soybean trifoliate, which approximated 0, 33, and 66% defoliation, respectively. Height and dry weight of all weeds were not affected by soybean defoliation level or defoliation stage. Soybean height 3 wk after defoliation at R5 was not influenced by weed interference, soybean defoliation level, or defoliation stage in either year. Averaged across soybean defoliation levels and stages in 1994, johnsongrass, common cocklebur, and hemp sesbania reduced soybean yields 30, 15, and 14%, respectively. In 1995, johnsongrass reduced soybean yield 35%. As soybean defoliation level increased, a linear decrease in soybean yield was observed. Averaged across weeds and soybean defoliation stages, 33 and 66% defoliation reduced soybean yield 6 and 20% in 1994 and 12 and 33% in 1995, respectively. Defoliation at R5 resulted in 10% lower yield than defoliation at R2 in one of two years. Yield reduction due to combinations of weeds and soybean defoliation was additive.

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