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Reports of Silk Clipping by Japanese Beetles

June 29, 2001
As I indicated in last week's Bulletin, Omar Koester reported the first Japanese beetles of the season in Monroe County on June 20, very similar to last year's first sightings of this insect pest. In general, only producers in eastern Illinois have had severe problems in cornfields and soybean fields with Japanese beetles. However, with each successive year, we seem to have increasing numbers of reports from producers in southwestern counties who are now battling this insect. This week Omar provided us with images of Japanese beetle adults feeding on corn silks. We have also received reports from Doug Gucker, Piatt County unit assistant, University of Illinois Extension, of Japanese beetle adults feeding on red clover blossoms, and Larry Martin, Monsanto, reported Japanese beetle adults in cornfields and soybean fields in Fayette and Shelby counties.

The Japanese beetle was first reported in the United States (New Jersey) in 1916. This insect pest has now spread into all states east of the Mississippi River, with the exception of Mississippi and Florida. Isolated pockets of Japanese beetles also have been reported in Missouri, Iowa, and Nebraska as well as California, where it was apparently eradicated. Although most of our readers are concerned with the injury inflicted on cornfields and soybean fields, Japanese beetles also are pests of many ornamental plants and fruit trees.

Like many of the other grub species that have plagued Illinois producers this spring, this pest promises to be no exception. In the coming weeks of July, corn growers are urged to monitor their pollinating fields for Japanese beetle adults and their silk clipping activities.

Japanese beetle adults feeding on corn silks. (Photo courtesy of Omar Koester.)

Japanese beetle adults on ear of corn with severely clipped silks. (Photo courtesy of Omar Koester.)

If silks are clipped to less than 1/2 inch in length, less than 50% of the plants have been pollinated, and three or more adults per ear are found, a rescue treatment should be considered. After anthesis, corn is less susceptible to damage; however, in August, producers will increasingly turn their attention to soybean fields and defoliation caused by this insect pest. Insecticides labeled and economic thresholds for both crops were presented in last week's Bulletin. Let us know what local densities of Japanese beetles are like in your respective areas of the state.--Susan Ratcliffe and Mike Gray

Author: Mike Gray Susan Ratcliffe

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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