Identification & Incidence: Corn root systems exhibiting injury ranging from scars to elimination of entire roots or nodes indicates presence of rootworms, which are small beetle larvae of either the western or northern corn rootworm leaf beetles. Injury occurs during June and early July following the hatch of larvae from overwintering eggs in the soil. Significant root injury will lead to lodging and a loss in yield. Adult rootworm beetles feed on foliage and silks from late July through September. Until recently, rootworm injury was limited to continuous corn, since rootworm beetle adults only deposited their eggs in corn fields. But, a new biotype of western corn rootworm, which deposits its eggs in soybeans, is now capable of causing significant injury to first year corn following soybeans. This new biotype, commonly called the first year corn rootworm, is a problem in some of the states west of Ohio but has not been found to be an economic problem in Ohio at this time.

Damaged root system

"Goosenecking" caused by larval damage

Sampling & Assessment: Potential rootworm injury may be estimated by monitoring the abundance of adult rootworm beetles from late July to early September in fields to be planted to corn the following year. Where corn is to be planted after corn, adult abundance may be evaluated by visual counts or by using yellow sticky traps. Where corn is to be planted after soybeans, adult activity may be evaluated by using yellow sticky traps.

Management Options: Where first year corn rootworm is not a problem, annual rotation of corn with an alternative crop will eliminate rootworm problems. If the first year corn rootworm is present, corn following soybeans may be susceptible to rootworm injury. Where a significant potential for rootworm injury exists in continuous corn or first year corn following soybeans, use of a soil insecticide (see chart) as a preventive treatment will reduce rootworm injury.