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Japanese Beetles Are Making Their Presence Known

July 6, 2001
We have received many reports of very large numbers of Japanese beetles in cornfields and soybean fields in several areas of Illinois. On June 28, Dale Burmester, Gateway FS in Red Bud, reported heavy infestations in cornfields in Monroe County, although he had not observed a lot of crop injury at that time. Several people in east-central Illinois have called in reports of Japanese beetles in crop fields and around homes where they are feeding on fruit trees and ornamentals. During a recent (June 28) drive through Douglas County, Aaron Hager, University of Illinois weed scientist, conducted an "unofficial windshield survey" and counted many pops as he tried to reduce densities of Japanese beetles there. However, Rick Reed, an aerial applicator stationed in Mattoon (Coles County) and a veteran of the "Japanese beetle wars" for many years, indicated on July 2 that he had not seen very many Japanese beetles yet, although he had sprayed one cornfield to prevent excessive silk-clipping injury. He expects to find more Japanese beetles in the near future, and I think he's right.

During the next few weeks in pollinating cornfields, watch for Japanese beetles (and corn rootworm adults) that might clip silks and interfere with pollination. If silks are clipped to less than 1/2 inch in length, less than 50% of the plants have been pollinated, and you find three or more adults per ear, an insecticide application may be warranted. Consider *Capture 2EC at 2.1 to 6.4 oz per acre; *Penncap-M at 2 to 4 pt per acre; Sevin XLR Plus at 1 to 2 qt per acre; or *Warrior at 2.56 to 3.84 oz per acre. Use of products preceded by an asterisk is restricted to certified applicators.

As almost everyone knows, Japanese beetles also will defoliate soybeans. Although the injury almost always looks worse than it actually is, large numbers of Japanese beetles can cause significant damage if defoliation exceeds 30% (field average) before bloom or 20% between bloom and pod fill. Again, adjust these thresholds according to the value of soybeans. If treatment is warranted, consider *Ambush at 6.4 to 12.8 oz per acre; *Asana XL at 5.8 to 9.6 oz per acre; *Penncap-M at 3 to 4 pt per acre; *Pounce 3.2EC at 2 to 4 oz per acre; Sevin XLR Plus at 1/2 to 1 qt per acre; or *Warrior at 3.2 to 3.84 oz per acre. Use of products preceded by an asterisk is restricted to certified applicators.--Kevin Steffey

Author: Kevin Steffey

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

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