Japanese Beetle Update

July 2, 2009

The first reports of Japanese beetles have been received. Bob Dodds the Lee County Extension Director and incoming Region 20* Extension Education Director reported a few Japanese beetles in his orchard on June 22. Duane Gissel, Extension Horticulturist in Scott County reported the first sighting of JB on the morning of June 29, and by that afternoon was flooded with calls from clients. Most reports were from areas where JB has more recently arrived and residents are not familiar with the pest (Blue Grass and the western parts of Davenport, and Eldridge).

The current, known distribution of JB in Iowa includes 38 counties (picture on right). The first issue with Japanese beetles will be the feeding by the adults on foliage, flowers and fruit. Linden tree leaves are one of the favorite foods of the adult beetles. See http://www.ipm.iastate.edu/ipm/hortnews/2008/7-30/update.html

Defoliation is usually not fatal to otherwise healthy trees. We usually don't know what stresses are occurring so there is no easy way to predict the tree's response to defoliation. Treating grubs in the turfgrass does not impact the beetle populations on the tree the following year. There are way more places for grubs to develop in the soil than can be treated, and the relatively small amount of the total population that is treated does not impact the overall population.

In addition to spraying trees two or more times with insecticide for contact control of Japanese beetles, many landscape maintenance workers are reporting good success using systemic insecticides, applied to the soil around the base of the tree at the start of the beetle appearance. The insecticide moves upward and into the leaves and kills the beetles as they feed. Some injury still occurs but less than if the tree is not treated. See http://web.extension.uiuc.edu/state/newsdetail.cfm?NewsID=13830

(*NOTE: For more information on the ISU Extension Restructuring see our web site at https://www.extension.iastate.edu/restructuring.htm)

Donald Lewis
Extension Entomologist
104 Insectary Building
Iowa State University
Ames IA 50011 USA