The Japanese beetle is a devastating pest of urban landscape plants. It was first found in Kentucky on the southern outskirts of Louisville (Jefferson County) in 1937. The isolated infestations were treated with insecticides and eliminated, delaying the spread of the beetle. However, populations in the region increased dramatically during the 1950s and ’60s; the Japanese beetle now occurs in all 120 counties in the Commonwealth.
Adult Japanese beetles are 3/8 inch long metallic green beetles with hard, copper-brown wing covers. Five small white tufts project from under the wing covers on each side, and a sixth pair at the tip of the abdomen. These white tufts help to distinguish them from similar metallic green or coppery colored beetles.
Adults emerge from the ground in late May or early June. Individual beetles live about 30 to 45 days with activity concentrated over a four to six week period. Beetle numbers begin to decline in late July but some can be found as late as September.
Japanese beetles can feed on about 300 species of plants, ranging from roses to poison ivy. Odor and location in direct sun seem to be very important factors in plant selection. The beetles usually feed in groups, starting at the top of a plant and working downward. While a single beetle doesn’t eat much; group feeding by many causes severe damage. Adults feed on the upper surface of foliage, chewing out tissue between the veins. This gives the leaf a characteristic skeletonized appearance.
Japanese beetles can fly as far as 5 miles but 1 to 2 miles is more likely. Usually, they make only short flights as they move about to feed. Local infestations spread as beetles move to favored food and egg-laying sites.
Many insecticides are labeled for Japanese beetle control on landscape plants. Examples include acephate (Orthene Turf, Tree & Ornamental Insecticide), carbaryl (Sevin and many other brand names), cyfluthrin (Bayer Advanced Garden Multi-Insect Killer Concentrate), lambda-cyhalothrin (Spectracide® Triazicide® Soil & Turf Insect Killer Concentrate), esfenvalerate (Ortho Bug-B-Gon Garden & Landscape Insect Killer Concentrate), and permethrin (Spectracide® Bug Stop Multi-Purpose Insect Control Concentrate and many other brands). Neem extracts (Bon-Neem) deter Japanese beetle feeding but may not be adequate against high populations.
Direct spray applications of insecticidal soap kills Japanese beetles on contact but does not provide any residual protection.
There is also the option of traps for Japanese beetles. Please make this note **DO NOT USE TRAPS** for this insect. The traps work very well, so well that they bring many, many more beetles into your yard, so just don’t use them.
For more information on Japanese beetles, or to get a copy of ENTFACT 409 – Managing Adult Japanese Beetles, please call the Fulton County Extension office at (270) 236-2351.