University of Illinois Extension

University of Illinois Extension

Hort Answers

Insect Damage

Corn Rootworm
Diabrotica virgifera (Western); D. barberi

Corn Rootworm damage. J. Schuster
Corn Rootworm damage. J. Schuster
5 (1 = rare 5 = annual)
4 (1 = very little damage 5 = plants killed)
Sweet corn

Plants Affected

The adult western corn rootworm is a yellow, 1/4-inch long beetle, with black stripes and a yellow underside. The adult northern corn rootworm is a greenish, 1/4-inch long beetle. The larva of each species is slender, white, and up to 1/2 inch long.

Adults feed on the green silks of sweet corn, preventing pollination and ear fill. They also damage cucumber and squash blossoms. Usually none of this adult damage is significant in commercial crops. The larvae feed on the roots of corn, reducing yield and causing stalks to fall over. This lodging can reduce yield if it occurs before pollination is complete.

Life Cycle

Western corn rootworm has one generation per year. Eggs are deposited in the soil from mid-summer until autumn. Generally the eggs start hatching from late May to early June the mid-west. Larvae feed on corn roots. The larvae have three instars then pupate in the soil. Later larvae (mid June through mid July) tend to cause the most damage. During this same time, adult beetles begin to emerge. The males emerge before the females. Towards the end of July, females begin to lay eggs with greatest amount of egg laying occurring in first half of August. The beetles feed on pollen, green silks, or leaves.

In much of the state, crop rotation (with corn following any crop except corn) prevents root damage from corn rootworms. In areas where the adults lay eggs in the soil of other crops, damage is likely even in rotated fields. Counts from yellow sticky traps during the latter part of the previous summer can be used to determine the need to treat. Apply a soil insecticide if corn is planted in the same field as last year and no earworm or corn borer control programs were followed. Where foliar insecticides for earworms or corn borers are used fairly often in sweet corn, they also control rootworm beetles and prevent egg laying.

Related Resources
Home, Yard & Garden Pest Guide
U of IL - Distance Diagnosis through Digital Imaging
U of IL - Plant Clinic