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

Prepare for Japanese Beetles

July 5, 2001

Once again it is time to think about Japanese beetles, which have become more common in Illinois in recent years. These insects appear in large numbers feeding on over 200 kinds of trees, shrubs, and flowers, primarily in July and early August. Some of the favorites include linden, maples, crabapple, elm, grape, and roses.

Adult Japanese 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. Feeding beetles skeletonize leaves, feeding on the leaf tissue between the veins. The remaining leaf turns brown and may drop.

Once they first appear, 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, which could potentially damage lawns later in the season. Japanese beetles overwinter as grubs in the soil, and emerge as adults again next summer to start the cycle over again.

Applying carbaryl (Sevin) or cyfluthrin insecticides to the foliage can control actively feeding beetles on flowers. On trees or shrubs, those same insecticides along with acephate (Orthene) or esfenvalerate may be used. Repeat if needed. 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.

Concerning grub potential grub damage to the lawn, adult beetles may appear in July but no lawn damage from grubs occurs later this summer. Only treat lawns for grubs if in fact grubs become a problem in the lawn. Monitor the lawn later this summer for browning areas and then check the root zone for any white grubs.

 

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