University of Illinois Extension
Bruce Spangeberg

These articles are written to apply to the northeastern corner of Illinois. Problems and timing may not apply outside of this area.

Stateline Yard & Garden

Japanese Beetle Problems

July 22, 1999

Depending on where you live in the northern Illinois, you may or may not have become familiar with the Japanese beetle over the past few weeks. This insect, which is gradually becoming more common in Illinois, may appear in large numbers feeding on various trees, shrubs, and flowers.

Don't confuse Japanese beetle with Asian longhorned beetle, a recent newsmaker in the Chicago area. The Japanese beetle has been in Illinois for some time and is gradually spreading west. Adult beetles are about 1/2 inch long and metallic green with copper-colored wing covers. Also look for white tufts of hair on the back end of the body. Japanese beetles are very active during the day and tend to appear in large groups on plants.

Japanese beetles feed on over 200 kinds of plants. Some of the favorites include linden, maples, crabapple, elm, grape, and roses, among others. Feeding beetles skeletonize leaves, feeding on the leaf tissue between the veins. The remaining leaf turns brown and may drop. Usually the upper portions of plants are damaged first because the beetles like warmth and sunshine. Aesthetic quality of the plant is reduced and it is subject to more stress as a result of the beetle feeding.

Adult beetles are usually out for about six weeks, which means most should be gone by mid-August. After mating, beetles lay their eggs in the soil. Eggs hatch into grubs that may feed on various plant or turfgrass roots. Thus it is possible for lawns to be damaged later this summer by the grubs. Japanese beetles overwinter as grubs in the soil, and emerge as adults again next June to start the cycle over again.

Actively feeding beetles can be controlled using carbaryl (Sevin). Repeat the application at about weekly intervals. Treatment is generally suggested for smaller plants, or perhaps those near entrances or other key landscape locations. Treating large trees is rarely suggested. Also, research has shown Japanese beetle traps to be ineffective, and may actually draw more beetles into the area.

Automatically treating lawns in areas where the beetles currently are feeding is not suggested. Only treat lawns for grubs if in fact grubs become a problem in the lawn. You may see adult beetles now on trees and shrubs but no lawn damage from grubs later this summer. And even if you were to kill all the grubs in the soil, there is no guarantee more beetles still don't appear next season on your trees and shrubs, as they fly in from other areas.


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