Issue 8, June 13, 2011

Japanese Beetle

Japanese beetle adults were found in Madison County on June 10 by Mike Roegge, Extension Educator. This is a little early for them to appear in the St. Louis area, although they are usually first found in southern Illinois in mid-June. Based on this observation, they are likely to appear in central Illinois during the third week of June and in northern Illinois at the end of June and early July.

Male beetles emerge first and wait for female beetles to emerge. They are apparently able to tell when and where a female is emerging from the soil as they are commonly noticed on golf courses milling about in small areas. Within minutes, an adult female will burrow its way out to be immediately mounted by numerous amorous males. Commonly, there are so many of these males that a roundish mass of them as large as a golf ball occurs. This phenomenon is called "balling."

Shortly after emergence, the beetles are soon noticed feeding on a variety of trees, shrubs, and other plants, preferring smartweed to most other plants. Monitoring smartweed as well as their balling activity on golf courses are excellent ways to discover early Japanese beetle emergence. Feeding is also heavy on linden, crabapple, birch, birch, rose, and willow, although many other plants are also attacked.

Adult feeding damage is of two types. Window-feeding occurs by the beetles eating the upper leaf surface and center of the leaf, leaving the lower surface intact. The resulting leaf is initially light-colored and semi-transparent, somewhat window-like. The exposed cells of the lower leaf surface soon die and turn brown, resulting in thin, brown leaves. Defoliation occurs from the beetles feeding on the leaf margins, frequently to the leaf midvein. When feeding occurs on both sides of the leaf, only the midvein is left, which soon dries and falls off. The beetles prefer sunny areas, feeding heaviest on the upper sides of leaves at the tops of trees and shrubs.

Japanese beetle adults are three-eighths to one-half inch long, stocky, and metallic green with copper-colored wing covers. They feed on a plant for about three days, and then fly a half-mile or more to a new host. Damaged leaves release odors that are attractive to these flying beetles, and leaves that have been damaged by Japanese beetles release odors that are even more attractive to Japanese beetles. Due to this, prevention of early damage reduces later damage.

Sprays of carbaryl (Sevin), cyfluthrin (Tempo), permethrin (Astro), or other labeled pyrethroid typically provides about two weeks of protection. With the adult beetles being present in damaging numbers for about six weeks, three applications every two weeks provides excellent control. If the client requests only one insecticide application, then the first one will provide the most control.

Similarly if clientele wish to control the beetles through hand-picking, starting when the beetles first appear is the most effective. In late afternoon and evening, a disturbed beetle will fold its legs and drop to the ground. Hold a wide-mouthed jar, such as a peanut butter jar, containing rubbing alcohol or soapy water under the beetle, poke at the beetle, and it will drop from the plant into the jar and be killed. Earlier in the day, disturbed beetles usually fly off rather than drop.

Repeatedly, research has shown that Japanese beetle traps result in more damage to plants near the trap than would occur than if no trap was present. The trap attracts beetles from other areas to its vicinity, but the beetles feed on nearby plants before flying to the trap. However, many people obtain satisfaction from trapping and killing the beetles that do enter the trap, making them feel that they are doing something to prevent damage. (Phil Nixon)

Phil Nixon

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