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University of Illinois Extension

Corn Rootworm

Corn Rootworm damage. J. Schuster

Corn Rootworm damage. J. Schuster 

Frequency

5 (1 = rare 5 = annual) 

Severity

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

Hosts

Sweet corn  

Symptoms

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 and northern corn rootworms develop through only one generation per year.  Eggs overwinter in the soil and hatch in early summer.  Larvae feed only on the roots of corn; if eggs hatch where no corn roots are present, they die.  Larvae pass through three growth stages before pupating in the soil and emerging as adults.  Females of both species lay eggs in late summer and fall in corn.  Over the last 15-20 years in Illinois and states to the east (where a corn-soybean crop rotation has been used widely), populations of western corn rootworms have exhibited a new behavior that is very important ... many female beetles are laying eggs in soybean fields – this means that when the eggs hatch the next year, the larvae will damage the corn planted in that field if a typical corn-soybean rotation is used. 

Management

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.


Filed under plants: Vegetables

Filed under problems: Insects Damage

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