The Japanese beetle is a minor pest in Iowa. Kevin Steffey, extension entomologist at University of Illinois, reported significant problems during mid-July in both corn and soybean, and 10,000 acres was sprayed for this pest in Illinois. In Iowa, Jim Fawcett, Iowa State University extension field specialist-crops, has found them again in soybean near Cedar Rapids in Linn County. Some fields have been sprayed because of defoliation. This year large populations of Japanese beetles have been found in Story County in central Iowa.
Rice, Marlin E., "Japanese beetles in corn and soybean" (2002). Integrated Crop Management News. 1782.