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The beetle invasion, Japanese that is, is underway

By Staff | Aug 19, 2011

Japanese beetles attacking soybeans.

URBANA, Ill. – The invasion of the Japanese beetle has begun. Row-crop producers and gardeners who haven’t seen them in their fields or backyards yet, won’t have long to wait.

“If you can keep feeding damage to a minimum when they first arrive, it is likely you will have less damage overall,” said Rhonda Ferree, a University of Illinois Extension horticulture educator.

“Japanese beetle traps are not recommended because the pheromone tends to bring more Japanese beetles into the area than are captured,” she said.

Control can be difficult because the beetles move frequently, Ferree said.

“Generally pesticide sprays, such as Sevin and Malathion, can reduce damage for several days, but several applications are required to maintain control.

Japanese beetles attacking corn.

Some gardeners find picking them off by hand every couple of days can be just as effective as spraying,” Ferree said. “When disturbed, the beetles fold their legs and drop to the ground. Hold a can containing rubbing alcohol or water with detergent below the infested leaves. The beetles will drop into the container and be killed.”

Prized roses and ripening fruit can be protected by covering with floating row covers, she added. “And there are a number of birds such as grackles, cardinals and meadowlarks that feed on adult beetles. These serve as natural enemies, which can also keep the use of conventional pesticides to a minimum.

“Above all, maintain the health of the plant,” Ferree said. “Plants damaged during the summer are more likely to suffer from other stresses, such as drought, early frosts, diseases and other insect attacks. Plants will often recover and appear fine next year, living on stored food reserves. But repeated defoliation in early summer will weaken many trees, shrubs and vines.”


The body of a Japanese beetle adult is one-half inch to three-quarter inches long with copper-colored wing covers and a shiny, metallic green head. A key characteristic is prominent white tufts of hair along their sides.

The adult beetle feeds on a variety of deciduous trees, shrubs and vines such as linden, Japanese maple, sycamore, birch, elm and grape.

The hardest-hit plants include roses, linden, birch, maple, viburnum, hibiscus, grapes, zinnia, canna, raspberries and apples.

Their favorite plants are rose and crabapple. They generally do not feed on dogwood, forsythia, holly and lilac.

Japanese beetle adult feeding damage is very distinctive. They skeletonize leaves by eating all the leaf tissue and leaving the veins.

Adults are most active from 9 a.m. to 3 p.m. on warm, clear summer days. Feeding is normally in the upper portions of trees.

Beetles prefer plants in direct sun, so heavily wooded areas are rarely attacked.

Adults are present for about six weeks from mid-June until early August.

After mating, females lay eggs in turf that hatch into grubs in August.

The grubs then feed on plant and turf grass roots until cold weather drives them deeper into the soil where they stay until emerging as adults again in June of the following year.

For more information on Japanese beetles or other horticultural issues, contact a local county Extension office.

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