Both adults feed on corn silks from August to the first frost. After pollination is complete, beetle feeding no longer poses a threat to yield. Crop rotation is recommended to control both species of rootworms . Since rootworms overwinter as eggs only in the soil of corn field, the pest is not present the first year a field is planted to corn. Continuous corn fields produce up to 4 million beetles per hectare.
Crop rotation is thus far superior to insecticides for reducing rootworm populations.
Recently the percentage of first-year corn in Ontario has been increasing. As a result, the number of hectares treated with rootworm insecticides in Ontario has declined significantly, and populations of rootworm beetles have also declined. If crop rotation is not practical and the western corn rootworm is predominant in your area, it may be necessary to treat 2nd-year corn, especially on clay soils. If extensive goose-necking occurs, consider treatment with insecticide the following spring. Calibrate the applicator each year, when switching chemicals or changing planting speeds.