RISK OF WESTERN CORN-ROOTWORM (COLEOPTERA, CHRYSOMELIDAE) DAMAGE TO CONTINUOUS CORN IN VIRGINIA

Information on the risk of western corn rootworm, Diabrotica virgifera virgifera LeConte, damage to continuously-grown corn previously was l acking in Virginia, as well as other mid-Atlantic states. A field stud y was conducted in 1993 and 1994 comparing root damage, whole-plant yi elds, and silage quality in insecticide-treated and untreated sections of 32 continuous corn fields in Virginia. Approximately 28% of the fi elds had serious root damage exceeding a rating of 3.5 (1-6 scale) in sections not treated with a soil insecticide. Also, 19% of the fields had an economic loss in whole-plant yield due to corn rootworm feeding damage. Silage quality, as evidenced by percent crude protein and aci d detergent fiber, was not significantly affected by corn rootworm fee ding. Because much of the continuous corn acreage in Virginia is treat ed preventively with soil insecticides for corn rootworms, the results of this study suggest that a large percentage of this insecticide use is unnecessary.