Japanese Beetles

Description: The adult Japanese beetle is broadly oval and nearly ½ inch long. The body is a bright metallic green with darker green legs. The wings are bronze colored and the beetle has white hairs just behind the wing covers and five patches along each side.

Symptoms: Japanese beetles are indiscriminate feeders, with a host range in excess of 300 plants. Both adults and grubs are destructive. Adults feed on the foliage and fruits of fruit trees, ornamental trees, shrubs, vines, field crops and vegetable crops. The damage left behind from adult beetles is skeletonized leaves and large, irregular holes. They usually feed in groups, starting at the top of a plant and working downward. The beetles are most active on warm, sunny days, and prefer plants that are in direct sunlight. A single beetle does not eat much; it is group feeding by many beetles that results in severe damage. The grubs develop in the soil and feed on the roots.

You are most likely to see the adults in late spring or early summer. During the feeding period, females intermittently leave the plants, burrow into the ground (usually in turf), and lay a few eggs. Normally she will lay 40 to 60 eggs this way per season. By mid-summer the eggs will hatch and the grubs will begin feeding on roots. Grubs are about 1 inch long and lay in a curled position. In late fall they burrow 4 to 8 inches down and remain inactive all winter. In early spring they return to root zones and resume feeding. They change into pupae in late spring and within 2 weeks become adult beetles which emerge from the ground.

Action: Many insecticides are labeled for use against adult Japanese beetles. Foliage and flowers should be thoroughly treated. The application may need to be repeated to prevent re-infestation during the adult flight period. Systemic insecticides also provide control of these beetles.

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