Issue 10, June 26, 2009

Japanese Beetles

Japanese beetle adults have emerged throughout southern and central Illinois. They were reported "balling" on turf in Urbana on June 22. Adult males emerge a couple of days before females. They are able to sense emerging females while they are still underground and tunneling to the surface. By the time that she emerges, she has attracted a crowd of males. As soon as she emerges, each male tries to mate with her, and of course only one succeeds. However, the others crawl onto her and each other, creating a ball of beetles that may be as large as a ping pong ball. Most of the females emerge over a couple of days and fly to trees to feed, causing the males to follow them. For that reason, "balling" on turf only occurs for about two to three days until most of the females emerge.

It is still too early to determine emergence levels in central Illinois, and we have not received any reports of emergence yet in northern Illinois. Emergence appears to be occurring as in an average year. The first Japanese beetle adults typically appear in central Illinois between June 18 and 24, so they are right on schedule. We do not expect adult emergence in northern Illinois until just after the July 4 weekend.

As reported earlier in this newsletter, we are cautiously optimistic that the long period of deeply frozen soil this last winter may have caused high mortality on the overwintering grubs. We do not expect any reduction in beetle numbers in southern Illinois.

Because Japanese beetle adults fly to new food hosts about every three days and are attracted to plants where Japanese beetle adults have previously fed, early control is important. Handpicking or spraying adults when they first appear on foliage will reduce early feeding damage, resulting in less damage through the season. Although they feed on a wide variety of hosts, smartweed, linden, crabapple, birch, willow, and rose are their favorites.

Effective insecticides include carbaryl (Sevin) and various pyrethroids including cyfluthrin (Tempo, Bayer Advanced Multi-insect Killer) and permethrin (Astro, Eight Insect Spray). Each application should provide ten to fourteen days of control. Because the adult beetles are heavily feeding for about six weeks, three applications two weeks apart should be sufficient.--Phil Nixon

Phil Nixon

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