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This NebGuide describes how counting western corn rootworm beetles throughout the summer can be used to determine the need for insecticide applications the following spring.
Western corn rootworms are one of Nebraska's most serious insect pests of corn. Eggs laid in the soil from late July through September overwinter and begin hatching in late May or early June. Larvae feed on corn roots, causing plants to lodge, and may reduce grain yields. The greatest injury usually occurs from late June to mid-July, when all corn roots may be destroyed if infestations are heavy. Fully grown larvae pupate in the soil and change into the adult beetle. Beetles emerge from pupae in the soil and are present in cornfields from early July until frost. Counting beetles in the cornfield throughout the summer will help you decide whether or not you need to use a soil insecticide if corn is to be planted in that field the following spring.