I have checked my plants in the Springfield area and so far, not too many. I know people in Beavercreek said they had high populations last year.
Japanese beetle adults have a wide appetite for plants, feeding on more than 300 species. Japanese beetles feed on flowers, leaves, and fruits. Their favorites include raspberries, grapes, linden trees, cannas, roses, and hibiscus.
The adult beetles feeding damage doesn’t kill a plant. It just looks horrible. The adult feeding is called skeletonizing. They eat all the green tissue on a leaf and the veins are the only part remaining. The leaves eventually dry out and fall.
The larva of the Japanese beetle is a grub. They feed on the roots of grasses and can eventually kill a lawn, particularly if there are heavy populations of grubs.
Adults hatch in late June and the adult feeding lasts sometimes until September. It’s not unusual to have a long adult emergence period instead of all at once.
The adults mate and begin egg-laying in July and August. The female lays up to 60 eggs several times in the top three inches of soil. The eggs may or may not survive depending on soil moisture.
If it’s really dry in August, eggs won’t survive. If lawns are moist or irrigated, eggs survive and grubs hatch after about two weeks and begin feeding.
August and early September is the most damaging time for Japanese beetle grubs. They go through three instars (growth stage) and go deeper into the soil to overwinter as a grub.
Their feeding on roots leaves distinctive dead patches (grayish grass) that pull up easily when tugged, just like carpet. You may see the grubs still feeding if it’s in late August and September.
Credit: Contributed
Credit: Contributed
A myth still prevails – if you eliminate the grubs, you eliminate the adults feeding in your landscape. This is not true.
They are very mobile and unless everyone in the neighborhood, city, and maybe state control the grubs, the adults will find the plants they like. In other words, if you have them, they will come!
Controlling grubs is helpful if you have high populations and the risk is high for turf damage. Controlling adults helps to knock down populations at times, but there are some years when no matter what you do, egg survival during the previous summer was high and adults follow suit.
Adult beetles can be sprayed with pesticides or knocked off the plants by hand into a bucket of soapy water. This depends on the population and your tolerance for them. I have a few flowering perennials that I protect but my linden trees, are on their own.
Pamela Corle-Bennett is the state master gardener volunteer coordinator and horticulture educator for Ohio State University Extension. Contact her by email at bennett.27@osu.edu.
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