What Are Japanese Beetles?
Japanese beetles can be a devastating insect to many plants in the landscape. The adult beetle feeds on leaves of many ornamental plants, including: crabapple, crape myrtle, linden, purple leaf plum, flowering cherry, and Japanese maple. This insect pest occurs in the Eastern U.S. (Northeast to Southeast and into the Midwest) but continues to move westward. The adult beetle is about 1/2" long with a bright metallic green head and mid-section. Coppery brown wings covers do not completely cover the body, leaving exposed a row of five spots of white hairs down each side of body.
Damage from Japanese Beetles
The Japanese beetle overwinters as a partially grown grub in the soil. In early spring, the grub resumes feeding on turfgrass roots. Pupation occurs near the soil surface where the grub transforms into the colorful adult beetle stage. Adult emergence occurs as early as the last of May in the Southeast and as late at mid-July in the Midwest.
On ornamentals, it is the adult beetle feeding on the leaves that causes damage. Beetles have tremendous appetites, feeding for 30-45 days. These beetles are leaf-skeletonizers, eating everything but the leaf veins, leaving a lace-like skeleton. Often the feeding becomes so great that plants look like they have been scorched by fire. This extensive damage not only reduces the plant's aesthetic value but also reduces plant vigor. The grub stage can seriously damage and kill large areas of turfgrass. Damaged turfgrass will easily roll back like a carpet.
Control of Japanese Beetles
Control of Japanese beetles can be very difficult for several reasons:
- Adult beetles are very mobile and can move in from non-controlled areas.
- Feeding occurs over a long time and on many plants.
- Japanese beetle populations can be extremely high.
- Some feeding may occur before control is achieved with certain pesticides.
- Grub control applications to the lawn will not eliminate beetles from the landscape.
- Chemical Control is the best means to minimize the damage caused by Japanese beetles. Since feeding occurs over a long time, more than one application may be required. Some pesticides will stop beetle feeding, but beetles may still be present.
- Traps are not successful in controlling Japanese beetles and may, in fact, encourage a greater number of beetles on a property.