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Home >> Departments/Offices >> Cooperative Extension >> Pest of the Month >> June 2

June 2

Japanese Beetles

Beginning in late May to early June, adult Japanese Bettles, which have metallic green and bronze bodies, can be found on leaves feeding so as to only leave the veins. The adults feed on many hardwood species of trees as well as the foliage and flowers of many other plants. Their larvae, or grubs, feed on roots of turf grass.

Sometimes it seems like an army has invaded, but there is only one generation per year. Most of the year is spent as larvae in the soil. During winter months the larva live about four to 12 inches below the surface. From early spring until May, they continue to feed on roots. Then the insects pupate near the soil surface. Adults fly in the daytime and are active on sunny, warm days for six to 12 weeks, beginning approximately the first week of June. Eggs are laid in the soil and larvae feed on the grass roots into the fall.

It is important to know that the beetles will not kill a plant. They may make it look ugly, but the plant will recover. So, one control option is simply to wait it out. The bulk of the adult population will be gone is six to eight weeks.

One of the simplist ways to remove these bugs from your yard is to use the handpick and destroy method. An easy way to do this is to walk around the yard with a bucket containing an inch of soapy water. When you see beetles, simply knock them into the bucket to drown. 

Many homeowners ask questions about traps. Japanese beetle traps are NOT recommended as they attract more beetles than they catch. You will be attracting beetles from your neighboring yards.

Chemical insecticides, in the form of granules or sprays, can be effective in controlling larvae in soil and turf, but not the adults. While there are insecticides labeled for adult control (such as carbaryl, also known as Sevin) they do not seem to be effective because of the shear number of beetles out at one time. Unless you have prize roses, a favorite food of the Japanese beetle, it is recommended to not apply any insecticides for Japanese beetle adults. 

Pesticide controls, such as imidacloprid, cyflurin and trichlofon, for the grubs, should be applied according to the label directions and should only be applied in September and in March.