By Erin Hodgson, Department of Entomology For the last few
weeks, I have been seeing Japanese beetle activity throughout
Iowa. Ornamentals, trees and shrubs have large numbers of adults
feeding and mating, and defoliation is becoming obvious in our
small plot research. In addition, ISU field agronomists have
been reporting defoliation in commercial soybean. Although
Japanese beetles have been reported here since 1994, plant
damage has been erratic. I strongly encourage growers and crop
consultants to scout corn and soybean fields for this pest this
year. Japanese beetles have one generation per year. Adults
emerge from grass in late June and begin to feed on low-lying
plants, and eventually move up on trees and field crops to feed
and mate. Mated females move back to grass in August and
September to lay small egg masses in soil cavities. The eggs
hatch into small white grubs that feed on roots underground
until late September when the temperature cools. The almost
fully-grown grubs burrow down in the soil and