YIELD RESPONSE OF CORN SUBJECTED TO WESTERN CORN-ROOTWORM (COLEOPTERA, CHRYSOMELIDAE) INFESTATION AND LODGING

Lodging of corn, Zea mays L., is often attributed to injury by larvae of western corn rootworm, Diabrotica virgifera virgifera LeConte. Because leaves of lodged plants exhibit vertical and horizontal spatial aberrations, yield may be adversely affected because of reduced photosynthetic efficiency. In a 2-yr study, we used a factorial arrangement of rootworm infestation (0 and 1,200 eggs per 30.5-cm row) and lodging treatments (lodged and upright) to determine effects on plant biomass and grain yield. In a second study, we examined how plants lodged from rootworm injury differ from upright plants with respect to plant and ear height, root rating, total leaf area, and vertical leaf area distribution. In 1987, rootworm-infested and lodged plants had significantly reduced plant dry weight and grain yield at nearly all sampling dates. Lodging treatments reduced grain yield of infested plants by an additional 11.9% over yield of upright, infested plants. In 1988, no differences in dry weight or yield occurred with infested plants, but lodging treatments reduced grain yield by 34.3%. In a severely lodged canopy, plant and ear height and light interception were significantly reduced in comparison with those of upright plants. Linear regressions of incident light versus leaf areas above each 0.31-m increment in the corn canopy resulted in significant slope (light extinction) differences. Because dry weight and yield were more consistently reduced by lodging than by rootworm infestation treatments, lodging must be an important factor in the relation between rootworm infestation and yield loss.