5 (1 = rare 5 = annual)

4 (1 = very little damage 5 = plants killed)

Sweet corn

Vegetable

• Sweet corn (Zea mays L. var. rugosa )

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.

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.

Home, Yard & Garden Pest Guide
The Home, Yard & Garden Pest Guide (C1391) provides is written for homeowners and other residents and provides nonchemical and current chemical recommendations for controlling pests associated with trees, shrubs, turf, flowers, groundcovers, vegetables, fruit, and houses. In addition, you'll find detailed information about integrated pest management, pesticide safety, and pesticide application and calibration techniques. This publication may be purchased at your local University of Illinois Extension Unit office, or by calling 800-345-6087, or by placing an order online (search for "C1391").
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U of IL - Distance Diagnosis through Digital Imaging
A free plant, weed, insect and disease identification service available through your local University of Illinois Extension office. Center Educators or State Specialists review & respond to information and digital images submitted by local Extension office personnel. Some samples may require further examination or culture work (nominal fee involved) at the U of IL Plant Clinic.
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U of IL - Plant Clinic
Services include plant and insect identification, diagnosis of disease, insect, weed and chemical injury (chemical injury on field crops only), nematode assays, and help with nutrient related problems, as well as recommendations involving these diagnoses. Microscopic examinations, laboratory culturing, virus assays, and nematode assays are some of the techniques used in the clinic.
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