RESPONSE OF HELICOVERPA-ZEA (LEPIDOPTERA, NOCTUIDAE) POPULATIONS TO CANOPY DEVELOPMENT IN SOYBEAN AS INFLUENCED BY HETERODERA-GLYCINES (NEMATODA, HETERODERIDAE) AND ANNUAL WEED POPULATION-DENSITIES

Field experiments to investigate the interactive effects among corn earworm, Helicoverpa zea (Boddie); soybean cyst nematode, Heterodera glycines Ichinohe; and annual weed species in soybean (Glycine max (L.) Merrill) were conducted during 1986-1988 in eastern North Carolina. This study examined the effects of canopy development in soybean on H.zea oviposition and larval establishment as influenced by H. glycines and weed densities. Soybean canopy development was inversely related to increasing initial population density (P(i)) of H. glycines. In general, soybeans with moderate and high H. glycines P(i) levels had more open canopies and consequently had greater H. zea larval populations during mid-to late August than did the 0 and low H. glycines P(i) treatments where soybean canopies were closed. In some field sites, very high H. glycines P(i) levels caused severe stunting and chlorosis, reducing the suitability of these soybeans as a food source for H. zea larvae. Weed-free and moderately weedy soybeans had greater H. zea larval populations than soybeans with high weed densities. Across locations and years, numbers of early developmental stages (egg and early instars) of H. zea were not influenced by H. glycines P(i) or weed density. Number of H. zea late instars were positively correlated with distance between canopies of adjacent rows.