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Japanese Beetle

Garden pest · Popillia japonica

Description​

The Japanese beetle is an introduced scarab beetle that feeds on many garden plants, including roses, grapes, beans, and fruit trees. Adults are about 10 mm long, with a metallic green head and thorax, copper-brown wing covers, and small white tufts along the sides of the abdomen. They emerge in summer and often feed in groups. Adults chew leaf tissue between the veins, leaving a lacy or skeletonized appearance. They may also damage flowers and the surfaces of ripening fruit. Females lay eggs in soil, especially turf. The larvae, called grubs, feed on grass roots and can leave patches of lawn that wilt or turn brown. Adults and grubs therefore cause different kinds of damage, and an adult seen on a plant does not necessarily explain a nearby lawn problem. Damage is often most noticeable when many beetles gather on a favored plant.

Symptoms​

  • Holes in leaves
  • Insects visible on the plant
  • Wilting

How to Identify​

Look for copper-brown wing covers, a metallic green head and thorax, and five white hair tufts on each side of the abdomen, plus two near the rear. Adults commonly cluster on sunny leaves, leaving veins behind as they feed; other leaf-chewing insects can make similar holes, so finding the beetle matters. In lawns, Japanese beetle grubs are creamy white, C-shaped larvae with brown heads. Other scarab grubs look much the same, and brown turf can result from drought or disease. Lift the edge of a damaged turf patch to check for grubs; identifying the grub species may require a local extension service.

Prevention​

Check favored plants regularly in summer so beetles can be removed before large groups gather. Where practical, protect vulnerable plants with fine netting or row covers before beetles arrive; remove covers when flowers need pollinators. Consider less-favored plants when replacing repeatedly damaged specimens, although no landscape plant is guaranteed beetle-proof. Avoid placing pheromone traps beside plants you want to protect: they can draw in more beetles than they catch. Keep lawns healthy through appropriate mowing and watering, but do not apply grub controls merely because adults are present. Adults can fly in from elsewhere, and many lawns tolerate some grubs. If turf has a history of grub damage, inspect the soil in late summer and choose controls only when grub numbers and damage warrant them.

Treatment​

Start by picking adults off plants in the cool of early morning and dropping them into soapy water. Repeat regularly while beetles are active. On small plants, netting can prevent further feeding, provided it does not block needed pollination. For severe adult damage, use only a product labeled for Japanese beetles and for the plant being treated; follow its directions and avoid spraying open flowers or foraging pollinators. Sprays may need repeating because new beetles can fly in. Treat lawn grubs separately, and only after confirming they are causing damage. Beneficial nematodes such as Heterorhabditis bacteriophora may help when applied to young grubs in late summer or early autumn; keep the soil moist and follow product temperature and application instructions. If stronger grub control is justified, ask a local extension service which registered products and application times work in your area. Grub treatments will not stop adults arriving from neighboring sites.

Plants Affected​

American Basswood, American Elm, Basswood, Black Cherry, Cherry Blossom, Chokecherry, Coneflower, Edamame, Elm, Grapes, Hibiscus, Littleleaf Linden, Red Mulberry, Red Oak, Redbud, Rock Elm, Rosa, Rose, Rose of Sharon, Rubus, Sand Cherry, Slippery Elm, Soybean, Vaccinium, White Mulberry, Wisteria, Zelkova

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