Relationship of Plant Phenology to Corn Yield Loss Resulting from Western Corn Rootworm (Coleoptera: Chrysomelidae) Larval Injury, Nitrogen Deficiency, and High Plant Density

Relationships among stresses caused by nitrogen deficiency, high plant population levels, and western corn rootworm (WCR) (Diabrotica virgifera virgifera LeConte) injury and their effects on phenological development and grain yield of corn (Zea mays L.) were determined in a 2-yr field study. WCR infestation did not significantly affect silk development in 1984, although yields were 88.8 and 80.6% of those of the control at densities of 600 and 1,200 eggs per 30.5-cm row, respectively. Effects from root injury appeared to be compounded by moisture-stressed conditions in 1985, and asynchrony between tassel and silk development resulted in increased plant barrenness. Grain yields in 1985 were 80.2 and 55.6% of those of undamaged plants at the 600- and 1,200-egg infestation levels. Evidence from plant density by rootworm interaction on silking interval, barrenness, and yields suggests that the corn plant can tolerate a certain amount of root damage when plant densities are low. A significant nitrogen by rootworm interaction on grain yields provided evidence that root injury interferes with nitrogen uptake. The disruption of phenology of the injured corn plants appeared to be the result of decreased plant turgor resulting from WCR feeding.