Description:
Adult beetles are ½ inch long and have green and copper bodies with white tufts of hair. Larvae can range in size from ½ to ¼ inch long and are white with brown heads. Adults will feed on foliage such as corn and soybean leaves until they lay eggs in the top four inches of the soil. Hatching larvae will feed on roots until becoming beetles and emerge from the soil to feed on foliage.
Scouting:
Japanese beetles are most prominent during VT through R1, but become active as soon as soils hit above 50°F. First, five days of silking is the most notable time for beetles to be present and commonly aggregate on the silks. End rows usually have the highest population of beetles as they move from field to field. Continued scouting is recommended as adults are highly mobile and can infect a field even after spraying.
Injury:
Japanese beetles will feed on corn plant leaves causing injury and opening up for diseases, but most of the damage is done by clipping silks during tassel. Stressed corn can react harder to this and have more of an effect on yield than healthy corn. Beetles will also affect soybeans by defoliation of leaves, starting with the top of the canopy and working its way down.
Management:
Spraying insecticide or incorporating insecticide with fungicide during spraying can help manage Japanese beetles. If three or more beetles are present per ear, silks are clipped to less than ½ inch, and pollination is less than 50% complete, spraying is recommended for corn. Management threshold for Japanese beetle in soybean is 30% defoliation before bloom and 20% defoliation after bloom.
