Many thanks to Sandy Mason, State Master Gardener Coordinator, for this timely and amusing article.
They're back and chewing on a rose near you. We usually see Japanese beetles the last week of June. However, this year many insects are arriving 10 to 14 days earlier, according to a June 18th article in the Home, Yard and Garden Pest Newsletter (http://www.ag.uiuc.edu/cespubs/hyg/) .
Adult beetles are attracted to other beetles and damaged leaves. Therefore, reducing feeding damage now can result in less damage later.
Japanese beetle adults are one quarter to one half inch long with copper colored wing covers, shiny metallic green head and prominent white tufts of hair along their sides; kind of attractive in a bugly sort of way.
They also have the munchies for your favorite rose, linden, grape, raspberry and some 350 different plants. They generally do not feed on dogwood, forsythia, holly, lilac, evergreens and hosta.
Japanese beetle adults feed on flowers and fruits and skeletonize leaves by eating all the leaf tissue and leaving the veins. Adults are sun lovers and are most active from 9am-3pm on warm, clear summer days.
Adults are present in high numbers for about 6 weeks into August. After mating, females lay eggs in turf. Female beetles prefer to lay eggs in moist, actively growing turf. Therefore, stopping or reducing irrigation during July results in reduced egg-laying, with fewer grubs. In other words, they are attracted to lush green lawns.
Unfortunately, controlling Japanese beetle grubs does not significantly reduce the number of adult beetles in your yard the following year. The beetles are good fliers and easily fly a couple miles in a single flight. They may travel 10 to 15 miles from where they lived as larvae.
Japanese beetle adults can be controlled with foliar applications of carbaryl or cyfluthrin. Each insecticide typically provides control for 10 days to 2 weeks, so at least three applications will be needed to protect plants from severe feeding damage. However, carbaryl is toxic to bees and other beneficials. Therefore, confine control of beetles to plants in important landscape locations or plants of particular value. Even though the damage caused by Japanese beetles looks unsightly, is usually doesn’t result in the death of trees and shrubs.
Neem or azadiractin is repellent to the beetles, but it appears to perform better when applied before the beetles become numerous and repeated applications are needed. Imidacloprid is also sold as a systemic to kill adult beetles in trees. For best effectiveness it should be applied in April or May when the trees are actively growing.
Picking beetles off by hand in early morning is another alternative. When disturbed, beetles fold their legs and drop to the ground. Hold a bucket containing rubbing alcohol or soapy water below the infested leaves. Move the plant and the beetles will drop to their death. Just make it a part of your early morning ritual; cup of coffee, cup of beetles. Just don't confuse the two.
Japanese beetle traps are not recommended where large beetle populations exists. Beetles tend to be attracted, but not caught in the traps.
If you have other questions about your garden or landscape, feel free to contact a master gardener at the University of Illinois Extension office in Charleston at 217-345-7034. You can also check out the many horticulture webpages at the U of I Extension’s website by visiting http://web.extension.illinois.edu/ccdms/ . And be sure to like the Master Gardeners’ new Facebook page, atwww.facebook.com/ColesCountyMasterGardeners.