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Japanese Beetles

A lot of attention recently has been on periodical cicadas, which are coming out of the ground after 17 years across parts of the Southeast and much of the Mid-Atlantic region. However, another insect is about to come out of the ground in South Carolina too, and this one is not just a novelty – it can completely defoliate many plants in your yard. That’s right, folks, it’s almost Japanese beetle season!

Japanese beetles (Popillia japonica) are native to Japan but have been in the U.S. for over a century. Although they are most common in the eastern part of the country, they are found in nearly every state and some parts of Canada. Adults are about 1/3 to ½ inch long with a metallic green head and bronze wing covers. There are five white patches along the side of the abdomen.

Adult Japanese beetle. Photo by David Cappaert, Bugwood.org.

Adult Japanese beetle.
Photo by David Cappaert, Bugwood.org

Most of the Japanese beetle lifecycle is spent underground. Adults lay eggs in the soil, usually in grassy areas, during mid-summer. From the eggs, grubs hatch and feed on the roots of grasses and other plants, eventually growing up to an inch long by the following spring. Feeding damage from the grubs can sometimes cause brown patches in turf. Grubs pupate in the soil, and adults emerge shortly thereafter and crawl to the surface, where they begin feeding and mating. Adults feed on the leaves of over 300 host plants, including trees, shrubs, and landscape and garden plants. Feeding damage can completely defoliate plants, causing trees and shrubs to look like they’re nearly dead. Populations seem to oscillate, meaning they go up and down and are higher in some years than others. This is likely due to weather patterns as well as a fungus that can kill some of the grubs while they’re underground.

Adult Japanese beetles mating on a knock-out rose. David Coyle, ©2021, Clemson University

Adult Japanese beetles mating on a knock-out rose.
David Coyle, ©2021, Clemson University

Unfortunately, options are limited when it comes to Japanese beetle control. If populations are low or if you don’t have too many susceptible plants, pick off the adults by hand. To be effective, this will have to be done daily (or a couple of times a day if populations are high). In some cases, a mesh layer can be used as a physical barrier to keep beetles off your plants – but if you have plants (like fruit trees) that require pollination, keep in mind that this mesh will also prevent pollinators from getting to the flowers.

Japanese beetle adult feeding. Photo by Steven Katovich, Bugwood.org.

Japanese beetle adult feeding.
Photo by Steven Katovich, Bugwood.org

Heavy feeding by Japanese beetle adults can result in plants having a brown appearance. Photo by Steven Katovich, Bugwood.org.

Heavy feeding by Japanese beetle adults can result in plants having a brown appearance.
Photo by Steven Katovich, Bugwood.org

Japanese beetle traps have gained popularity recently, but research shows that they tend to attract more beetles than they capture. For this reason, Japanese beetle traps are not recommended.

Insecticides are the most effective way to control both adults and larvae, and there are many different types that will work. For information on grub control, see HGIC 2156, White Grub Management in Turfgrass. Adults can be controlled with formulations containing imidacloprid, dinotefuran, or several other chemical formulations. When applying chemicals, always read and follow label directions. CAUTION: Take note of pollinator protection restrictions.

If this document didn’t answer your questions, please contact HGIC at hgic@clemson.edu or 1-888-656-9988.

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