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Japanese Beetle News

Current information for homeowners and agricultural producers

News Release on Japanese Beetle Invasion


The invasion of the Japanese beetle has arrived in west central Illinois. According to Rhonda Ferree, extension educator in horticulture, her office has received a flurry of calls, emails, and Facebook posts about this insect pest. If these beetles aren't causing plant havoc in your area, just wait.

Japanese beetle adults have a 1/2 to 3/4 inch long body 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 a variety of deciduous trees, shrubs and vines such as linden, Japanese maple, sycamore, birch, elm, and grape. Hardest hit include roses, linden, birch, maple, viburnum, hibiscus, grapes, zinnia, canna, raspberries, and apples. Their favorite plants are in the rose family including 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 9am-3pm 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 which hatch into grubs in August. The grubs then feed on plant and turfgrass roots until cold weather drives them deeper into the soil where they stay until emerging as adults again in June of the following year.

Control can be difficult because the beetles move frequently. Generally pesticide sprays, such as Sevin and Malathion can reduce damage for two to several days, but several applications are required to maintain control. Some home gardeners find picking them off by hand every couple of days can be just as effective as spraying. Ferree says that, "If you can keep feeding damage to a minimum when they first arrive, it is likely you will have less damage overall."

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.

Japanese beetle traps are not recommended because the pheromone tends to bring more Japanese beetles into the area than are captured.

The underground grub stage of this beetle feeds on turfgrass roots. If populations are high enough, control may be needed to protect your grass. However, according to Phil Nixon, extension entomologist, controlling Japanese beetle grubs does not significantly reduce the number of adult beetles the following year. The beetles are good fliers and easily fly in from other areas.

A number of birds such as grackles, cardinals and meadowlarks feed on adult beetles. Two native predator insects and a couple of introduced parasites may help to keep Japanese beetle populations in check. Protect natural enemies by keeping the use of conventional pesticides to a minimum.

Above all, maintain the health of the plant. 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.

For more information on this or other horticultural issues, contact your local Extension office by visiting www.extension.illinois.edu. You can also post questions on Rhonda's facebook page at www.facebook.com/ILRiverHort.



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