Japanese Beetle

Insect Identification

Images

Adult Japanese Beetle

Damage

The Japanese beetle is known for causing substantial damage to the leaves of a wide variety of plants. The most obvious sign is the appearance of holes in the leaves in between the veins. The result is a lacy appearance of the leaves. The adult beetles do not hide on the underside of the leaves, so they should be easy to spot.

Affected Plants

The Japanese beetle damages the plants listed below

Soybeans

Management

Control techniques are listed in order of effectiveness.

Row covers

If possible, completely cover affected plants early in the season and keep covered as long as beetles remain a threat.

Physical removal

Crush the adults by hand starting in early summer. Vigilant monitoring and aggressive control early in the season will significantly reduce their numbers.
If early-season controls are properly implemented, only periodic monitoring will be required for the remainder of the season.

Insecticides

Only begin using insecticides when you become overwhelmed with high numbers of beetles and physical removal is no longer practical. The first of two options kills any Japanese beetle that eats a sprayed leaf. The second option only kills a beetle that has been directly sprayed.
- Bacillius thuringiensis var. gallariae (Btg)
- Insecticidal soap

Predators

Beneficial nematodes can be used to control Japanese beetle grubs in an area. However, spreading them in your plot will not prevent the overwintering grubs in other plots from spreading to yours.

Traps

Japanese beetle traps are unlikely to do anything to control beetle numbers and mostly serve to increase numbers in the vicinity of the traps.
In some instances, they can be a good way to monitor beetle populations. If this is your intent, place them on the outskirts of the affected area and check the traps daily. When you start catching beetles, remove the trap and dispose of it. Begin spraying an organic insecticide such as Btg on the affected plants.