Tuesday, August 04, 2009

Viburnum Leaf Beetle Confirmed in Illinois

Last week, the Viburnum Leaf Beetle was confirmed in Illinois for the first time. A few beetles were positively identified on a viburnum planting in Cook county. This invasive beetle is native to Europe and is currently found in New York, Maine, Massachusetts, Pennsylvania, and Ohio.It was also found for the first time in Wisconsin this past May.

This pest has the potential to become a serious problem in nurseries and landscapes. Both the adult and larval stages of the viburnum leaf beetles can be severe defoliators. Larvae and adults feed on the leaves, defoliating between the midrib and larger veins. Heavy infestations can defoliate shrubs, cause dieback, and eventually kill the plants. It is the only pest known to skeletonize viburnum leaves.

Viburnum leaf beetles overwinter as eggs on twigs of the host plant. Eggs hatch in May of the following year. Larvae begin feeding on the host plant; they are usually found feeding in groups. Between early and mid-June, larvae drop to the ground and pupate. They remain in the ground for about 10 days. Adult emergence generally occurs from mid- to late July. Adults will remain active until the first frost. Development from egg to adult takes eight to ten weeks.

After emergence adults feed on leaves, leaving irregular circular holes. In late summer and fall, females will begin laying eggs. They chew holes in the bark of twigs to deposit eggs and then cover them with excrement and fragments of chewed bark. A female can lay up to 500 eggs.

Viburnum leaf beetle adults are ¼ to 3/8 inch long, yellowish brown to light brown in color. When held in the sunlight, they have a sheen that is the result of a golden-grey pubescence. Larvae are larger than the adults (~1/2 inch), greenish-yellow to white, and covered with dark spots.

Feeding is limited to species of viburnum. The viburnum leaf beetles have a preference for viburnums with little hair (pubescence) on the foliage, including the European cranberrybush viburnum, arrowwood virburnum, and American cranberrybush viburnum. They also feed on wayferingtree viburnum, Rafinisque viburnum, mapleleaf viburnum, nannyberry virburnum, and Sargent viburnum.

Resistant varieties include Koreanspice viburnum, Burkwood viburnum, doublefile viburnum, Judd viburnum, lanatanaphyllum viburnum, and leatherleaf viburnum.

The most effective management strategy (for small plantings) is to prune out and destroy infested twigs. This is best accomplished after egg laying in the fall and before hatch occurs in the spring.


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