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Wednesday, July 9, 2008 08:17 pm

More beetle mania

Early removal by hand is an effective way of controlling these noisome pests

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Japanese beetle adults are munching on roses, lindens, raspberries, and apple trees in your neighborhood. These voracious foliage and fruit feeders, which dine on nearly 300 species of plants, are busiest from late June until mid-August. The Japanese beetle, Popilia japonica Newman, is metallic green with coppery wing covers. The half-inch-long beetles chew the leaf tissue between the veins, leaving a skeletonized leaf. Adults most actively feed between 9 a.m. and 3 p.m. on warm, sunny days. Normally they start feeding on the upper portions of a plant and work downward. Japanese beetles prefer plants exposed to direct sunlight.
A native of Japan, the Japanese beetle first popped up stateside in New Jersey in 1916, at a nursery. Apparently it made the trip as a grub in the roots of imported irises. It didn’t take long for people to recognize that it was a serious threat to agriculture. Early efforts to eradicate it were unsuccessful; by 1920 the beetle occupied 50 square miles. Today the Japanese beetle can be found in every state east of the Mississippi. Because it is an introduced species, the Japanese beetle has no natural predators in the U.S. The primary natural predator in Japan is the winsome fly, a parasitic insect. Attempts at establishing this predator here have met with limited success. Damage to trees and shrubs is considered to be primarily aesthetic. “Even heavily attacked trees and shrubs rarely exhibit severe dieback, because the beetles attack after the bulk of food production has already occurred in the leaves,” says Phil Nixon, an entomologist with the University of Illinois Extension. “Photosynthetic production primarily occurs early in the season, when the leaves are still soft and pliable. Japanese beetle defoliation occurs later in the growing season. This allows one to selectively treat those trees and shrubs in very obvious landscape locations and to ignore the damage on others.”
There are several control options for Japanese beetles.
• Because the adult beetles prefer foliage previously damaged by other Japanese beetles when they change hosts, early removal of beetles by hand is effective. In the late afternoon and evening, disturbed beetles fold their legs and drop to the ground. By holding a container of rubbing alcohol (isopropyl alcohol) or soapy water under beetles and poking at them, one can easily collect a pint or so in less than an hour. If this is done every day or two for the first couple of weeks after the beetles emerge, subsequent damage through the summer is reduced. Although labor-intensive, hand removal is a viable option. • Netting is used to provide complete protection. Rosarians protect prize individual buds and blooms or even entire plants with netting. Backyard blueberry growers use netting as well. Shadecloth with a high light transmittance, spun-bound polyester row covers, netting sold in fabric stores, window screening, and other meshes all work well. • Insecticides provide effective control of adult Japanese beetles. Heavily attacked ornamental plants can be sprayed with carbaryl (Sevin), cyfluthrin, and permethrin. Always read and follow label directions for safe use of pesticides. Sevin is toxic to bees and other beneficial insects and should be sprayed in the evening. Protect natural enemies such as birds and predator insect by keeping the use of conventional pesticides to a minimum. Spray only plants where damage is very noticeable or food crops that are under attack. Plants in less obvious parts of the landscape and large trees can go untreated. Imidacloprid (Merit, Bayer Advanced Garden Tree and Shrub Insect Control) moves systemically through the tree to provide control. Soil applications require two months to move through the tree and so are not practical now for this year’s infestation. Once in the tree, the imidacloprid should be effective for at least a year.
• Traps are available that contain a pheromone (externally produced hormonelike chemical) attractive to male Japanese beetles and a floral lure attractive to female beetles. The pheromone traps are useful for detecting beetle emergence but are not recommended as a control measure. Research shows that beetles are attracted from a considerable distance to areas near the traps but then switch their seeking behavior to food plants, resulting in heavier plant damage near traps.
The good news is that adult Japanese beetles seem to be emerging slowly this year.
If you’re looking for gently used garden tools, outdoor furniture, and other garden-related goods, be sure to attend the Garden Shed Sale, sponsored by the master gardeners of the U of I Extension’s Sangamon-Menard Unit. The sale will be held from 5-7:30 p.m. Thursday, July 17, at the extension’s office at the state fairgrounds. Admission is free.
Also that evening, master gardeners will offer walking tours of the demonstration gardens. For more information, call 217-782-4617 or go to
Jennifer Fishburn is a horticulture educator with the University of Illinois Extension Sangamon-Menard Unit. Contact her at


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