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Japanese Beetles

JAPANESE BEETLES
By George Piasecki 1992 Newsletter

It was a very rare day in our office last summer if someone did not call for advice and assistance for Japanese beetles. The adult beetle that devoured the foliage of ornamental trees is oval, approximately ½ inch long, has a metallic green and copper back and is considered to be very attractive, until you see the damage it causes.

As the name suggests, the beetle is native to Japan, imported to the U.S. in 1916 by way of New Jersey, and is now established in almost every state east of the Mississippi.

The entire life cycle of the Japanese beetle requires one year to complete. The beetle overwinters as a grub (larva) in the soil below the frost line. In spring, grubs begin feeding on grass roots as they work their way toward the soil surface. After pupation in mid-June, flying adults emerge and begin feeding on the leaves of as many as 275 different kinds of trees and shrubs, creating a lacy and skeletonizing pattern. Favorite foods are rose, cherry, peach, crab apple, plum, linden, Japanese red maple, and certain azaleas.

Adults usually live anywhere from 30 to 45 days. Females feed, mate, re-enter the soil, lay an average of 6 eggs, then return to feed. These periods of feeding and egg laying continue until a total of 40-60 eggs have been deposited. In 10-12 days, the eggs hatch into tiny grubs. These grubs feed on grass roots until cold weather arrives, then move down into the soil to overwinter starting the cycle all over again. Fully grown beetle grubs are grayish-white with brown heads, ¼ inch in diameter, and ¾ to 1 inch long and can be found just under the grass layer in their characteristic “C” shaped position. During this grub stage, beetles can do extensive damage to lawns. As the roots are eaten, the grass turns brown and dies, and will pull up like an old doormat. Before you know it, the damage has been done and overseeding is needed to re-establish the lawn. Often, symptoms won’t show up until it’s too late to treat the cause.

Controlling grubs and adult beetles can be difficult. Predation by birds, moles, shrews. and skunks provide very little control. Applications with sevin or a host of other stomach/contact insecticides work well on active feeding adults, but results are limited as most pesticides remain effective for only 7 to 10 days. Due to continuous migration of adult beetles, additional applications may be needed in areas where population levels are high. In low population areas, plants will tolerate a moderate defoliation and one application may suffice.

“Bag-a-beetle” traps baited with a sex attractant can be used in place of insecticides. For best results, the traps should be placed on the edge of the property and downwind from any desirable plants as they “attract” beetles. These traps will help in reducing the adult population but they should not be relied upon for total beetle control.

In 1991, the combination of adult beetles and hot, dry weather during the summer created ideal conditions for grub infestation and damage should be expected for 1992. Consistent applications of granular oftanol in early spring and granular diazinon in late summer provide good control. For best results, these granules should be watered in after their application. The use of milky spore disease for grubs was thought to be a good biological control method, however, studies at the University of Kentucky during the 1980’s proved that milky spore had little to no effect on the adult population over an extended period of time.

During our seasonal visits to your property, SPS technicians will note any problems that they see; however, sometimes new infestations will appear in between our scheduled visits. You can help us by calling and reporting any infestation that may occur so the we may schedule an immediate application. Look for Japanese beetles to appear in mid-June.