By: Paul Markworth, Board Certified Master Arborist WI-0153B
Roving gangs of Japanese beetles have decimated the leaves on many trees, shrubs and perennials in our landscape this past summer. The Japanese beetle is another exotic insect that has made its way to this country and can be a devastating pest to our landscape. In ten or twenty years we may look back and decide that the Japanese beetle is a more destructive insect than the Emerald ash borer.
The adult metallic green half-inchlong beetle is a voracious foliage feeder of more than 300 species of plants. Japanese Beetles feed on the upper surface of foliage, chewing out tissue between the veins, leaving a netted/ lacy appearance. This can be seen through the fall until leaf drop. The larval stage develops from eggs laid in the soil and feeds primarily on the roots of grasses, but will also feed on the fine roots of shrubs and trees.
While Japanese beetles will feed on most any plant, their favorites are European lindens, white-barked birches, Japanese maples, crabapples, cherries, willows, elms, roses and grapes. Diseased and poorly nourished trees and plants are especially susceptible to Japanese beetle attack.
The adult beetles can fly one to two miles at a time and generally fly around in swarms going from one tree to another and one property to another. This makes control difficult as one day the “south-side gang” can be in your yard and a week later the “west-side gang” may show up. This is what makes the control of this insect so challenging.
A soil application of a systemic insecticide in fall or early spring reduces the amount of defoliation caused by the adults. In years where adult populations are very high, noticeable damage may still occur because the insect does have to feed a little to ingest the insecticide. When neighboring gangs move in, increasing feeding pressure even more, an additional treatment with a foliar spray may be called for.
If you have trees that that were attacked by Japanese beetles this year or live near a golf course (Japanese beetles like to lay their eggs in irrigated turf), call your Wachtel Certified Arborist to get set up with a control program.
© Copyright 2008 – Wachtel Tree Science & Service, Inc.