Japanese beetles evident in midsummer
It is usually midsummer when we start to see many trees, shrubs and vegetable plants in the landscape with skeletonized, chewed leaves - some nearly completely defoliated by August.
Japanese beetles are the main culprits and can often be found on roses; cherry, apple, birch, elm and linden trees; and zinnias, ivy and marigolds. The adults feed on nearly 300 host plants. They were first found in the United States in 1916 near Riverton, N.J. Strategies to manage the larval and adult stages are estimated to cost more than $460 million each year.
In order to properly control Japanese beetles in your garden or landscape, you must first understand its life cycle. The beetles overwinter as larvae (white grubs) in the soil. As the weather warms in the spring, they move toward the soil surface and feed on grass roots. Larvae mature in late May through June and molt to pupae in the soil. A good indicator of a grub problem is night time digging and feeding by skunks on your lawn.
Once the Japanese beetle adults emerge from the soil in late June, they begin to feed on ornamental plants, chewing foliage between the leaf veins or skeletonizing it. The best way to control Japanese beetles is not to attract them to your yard with a "Bag-a-Bug" device which contains a synthetic sex attractant or lure. Those devices were originally designed as a monitoring device and will probably attract more Japanese beetles to your yard than you already have.
Control strategies should be targeted at the next generation that will begin to hatch and feed in the lawn in late summer. Several biological controls exist, including parasitic nematodes, or Milky Spore, a fungus that will attack the grubs in the soil. Insecticidal control measures can be applied to your lawns in late summer or early fall. It is best to apply materials late in the day because grubs move up in the soil to feed during the evening.
If you have grub problems, avoid the desire to "attract and bag" them and prepare to control them in the turf later this summer when they are young, hungry and vulnerable.
For more information on Japanese beetle control measures, visit http://extension.psu.edu/plants/gardening or call the local Extension office. In Lackawanna County, call 963-6842.
VINCENT COTRONE is an urban forester with Penn State Cooperative Extension.
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