REDUCTIONS IN SOYBEAN YIELD AND QUALITY FROM CORN-EARWORM FLOWER FEEDING

Soybean, Glycine max (L.) Merr., defoliation and pod feeding by corn earworm, Helicoverpa zea (Boddie), are often considered types of injury that lead to yield and quality reductions. When infestations coincide with the flowering period, however, density of H. zea larvae is higher on flowers than on other plant parts. Experiments were conducted to assess yield reductions relative to H. zea feeding on flowers, foliage, and pods. Populations of H. zea were manipulated with insecticides at two locations in 1983 and 1984 to achieve varying densities in soybean. Flower numbers, leaf area, and pod numbers were reduced in treatments with larger populations of corn earworm larvae. In addition, fewer flowers were shed from plants with large H. zea populations, and in one trial, pod shed was also decreased. Flower removal by H. zea larvae resulted in a delay in pod set. At harvest, the number of seeds per pod was reduced in three trials that had the largest H. zea populations. Seed weight was increased or decreased by H. zea injury. Injury by H. zea sometimes increased percent soybean seed protein and sometimes reduced harvestable yield. Flower feeding contributed to yield losses by delaying pod set.