Field studies were conducted to determine the effect of several herbicides on soybean thrips numbers in soybean. Adult soybean thrips numbers in the preplant-incorporated and preemergent herbicide treatments were observed to be either greater than or equal to, but never less than, numbers in the control plots. Larval soybean thrips numbers were not observed to be affected by the preplant-incorporated or preemergent treatments. The postemergence herbicide treatment of naptalam plus dinoseb consistently reduced both adult and larval soybean thrips numbers. The other postemergent treatments did not affect numbers consistently.

Field studies were conducted during 1983 and 1984 to determine the single and interactive effects of trifluralin, soybean thrips, and the sodium salt of acifluorfen on soybean. Increased soybean injury was observed in 1983 when acifluorfen at 0.6 kg ai/ha was applied to soybeans infested with soybean thrips versus plants where soybean thrips were controlled. Soybean injury measured by percent defoliation and visual injury ratings was reduced when thrips were controlled versus soybeans where thrips were not controlled with carbaryl at 0.9 kg ai/ha in 1983. Soybean thrips alone did not reduce soybean seed yield in this study. Acifluorfen reduced soybean photosynthetic rate, shoot weight, root weight, and seed yield. Trifluralin had no effect on soybean growth parameters measured in this study.