Western Corn Rootworm and Japanese Beetle Adults Becoming Active

Western Corn Rootworm and Japanese Beetle Adults Becoming Active

June 29, 2012
Corn rootworm damage
Figure 1. Corn leaf damage caused by western corn rootworm.
Japanese beetle
Figure 2. Japanese beetle

We have received reports of western corn rootworm beetles emerging in southeast and south central Nebraska over the last two weeks. This is earlier than we normally see them. When rootworm beetles emerge before silking, they may feed on the surface tissue of corn leaves, scraping away the green tissue. As soon as silks emerge, the beetles will move to those tissues which are highly preferred for feeding.

Japanese beetles have been emerging over the last week or so. We have received reports in the past of Japanese beetles feeding on crops in parts of Hamilton and Saline counties. Japanese beetles may feed on soybean leaves and corn silks. Entomologists in states east of Nebraska report that Japanese beetles may also feed on corn leaves if silks have not emerged, producing similar damage to that caused by western corn rootworms.

Treatment Thresholds

Damage in soybeans should be evaluated in relation to other defoliating insects in soybeans. Consider treatment if defoliation in vegetative soybeans will exceed 30% and insects are present (20% threshold in reproductive stage soybeans).

A variety of effective insecticides are available; make your choice based on the insect complex present in your fields. See treatment guides on the Department of Entomology  website for a list of insecticide rates and restrictions for use against defoliating insects in soybeans.

Bob Wright
Extension Entomologist