Japanese Beetles Are Making Their Presence Known in Soybeans

July 2, 1999
In last week's issue of the Bulletin (issue no. 14, June 25, 1999), I wrote an article about Japanese beetles having been observed in a cornfield in Lawrence County. Many other folks now are finding Japanese beetles in soybean fields, and the injury is quite noticeable in some areas. Joe Spencer, research entomologist with the Illinois Natural History Survey, collected 147 Japanese beetles in 100 sweeps in a soybean field near a research trial area in Champaign County. He also observed a lot of skeletonized soybean foliage.

Japanese beetles feeding on soybean leaf.

I won't repeat the description of the Japanese beetle provided in last week's Bulletin; most people in eastern Illinois are familiar with these showy insects. Also, they often appear in large numbers in relatively small areas, so they are difficult to ignore. Their defoliation results in a characteristic lacy appearance to the injured leaves. Although their appearance in soybeans often sets off an alarm among a lot of people, the amount of injury often is overemphasized. Treatment is not warranted during vegetative growth until defoliation reaches or exceeds 40 percent. However, the economic threshold is 15 to 20 percent defoliation during flowering, pod set, and pod fill. Remain vigilant for Japanese beetles and other soybean defoliators as the time for flowering approaches.--Kevin Steffey

Author: Kevin Steffey