Japanese beetles have been in Missouri since 1934, but remained in urban areas before moving to rural areas in southern and central Missouri in the late 1990s. In recent years they are being found in northern Missouri as well. The adults are bright, metallic green insects with bronze or copper-colored wing covers and are approximately one-half inch long. The adults emerge from the ground in late June and early July and are found for 45 to 60 days.
Adults prefer to feed on plants that emit a strong odor including many flowering shrubs, roses, hibiscus, grapes, raspberries, blackberries and other trees with mature fruit; but they will feed on over 400 vegetable and ornamental crops.
After mating, the adult females burrow into the soil and lay eggs. Eggs hatch and white grubs grow throughout the late summer months in the top 5 to 15 inches of soil, overwintering the soil.
In the spring, the grubs pupate and adult beetles emerge. Dr. Kevin Rice, MU Extension Entomologist says that drought conditions the previous year can reduce the number of beetles that emerge, but wet conditions do have an impact the following summer.
Japanese beetles will feed on field corn and soybeans. Generally, damage is limited to field borders where they congregate. If Japanese beetles are found in corn, insecticide application is warranted when there are three or more beetles per ear when silks are present and pollination is less than 50% complete. Feeding at other times during the season usually does not cause enough damage to have an economic impact on corn. If more than 30% leaf defoliation is occurring in soybeans before bloom or 20% defoliation is occurring during flowering and pod fill, insecticide treatment is necessary to prevent economic loss.
For more information contact Valerie Tate, field specialist in agronomy at email@example.com or call 660-895-5123. University of Missouri Extension programs are open to all.