Japanese beetles threaten crops in Iowa and Minnesota

Japanese beetles are causing extensive damage to fruiting trees and other plants across southwest Iowa, feeding on leaves of roses, grapes, apple and cherry trees, raspberries and corn silks. Damage is most severe on young or stressed plants, while mature trees can tolerate more loss. Residents are advised to shake insects into soapy water, use netting (avoiding flowering periods), and apply garden insecticides only when necessary.

In Minnesota the beetles remain established, especially around the Twin Cities and southeast. A tiny parasitic fly, the Winsome fly, released by state and federal agencies from 1998 to 2006, is now adapting to local conditions and may help suppress beetle populations. Researchers highlight the potential of this biological control to reduce reliance on chemical treatments and protect both ornamental and food crops.