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Japanese Beetle

July 7, 1999

Japanese beetles are out in force throughout Illinois, and large numbers are being reported in the southwestern, central, and northern parts of the state. Feeding damage is heaviest at the top of the plant. There the leaves may be lacelike from feeding holes, or brown because the upper surface and interior have been eaten away, leaving the lower surface, which dries and turns brown. Remember that repeated insecticide treatments are needed to minimize damage, but damage rarely seriously harms the health of attacked plants.

Control beetles on shrubs and small trees near main building entrances and other important landscape locations where the damage would be obvious. Beetles damaging taller trees and in less obvious areas of the landscape can usually be ignored. Research has shown that using Japanese beetle traps actually results in more damage than not using them. These traps attract beetles from other areas, but many beetles are not attracted all the way into the traps.

Controlling the larval form as white grubs feeding on turf roots does not significantly reduce the number of adult beetles in the landscape the following year. Adult beetles are very good fliers, and they easily fly in from other areas. Only treat turf areas for grubs if conditions are right for damage to occur from the larval feeding.

Author: Phil Nixon staff at The Morton Arboretum


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