2007 Year in Review

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Elm Leaf Beetles




Elm leaves may be dropping as the result of feeding by elm leaf beetles. A serious defoliator of elms throughout the United States, elm leaf beetles have a preference for Siberian elms, which are often incorrectly called Chinese elm. Elm leaf beetles are strictly leaf feeders and do not carry the fungus responsible for Dutch elm disease.

Elm leaf beetles made their first big appearance in early summer. Like boxelder bugs, they over-winter as adults and sought shelter in places such as homes, outbuildings, or under loose tree bark. In some cases, they became a nuisance indoors during the "moving in phase" in the fall or in the spring when they migrated outdoors.

The adult beetle is yellowish to dull-green, about 1/4 inch long, with a black stripe along each side of the body. Adult beetles left over-wintering sites in early spring and migrated to area elms. Once in trees, the adults began to feed on foliage, mate and lay eggs on the leaves.

The lemon-colored eggs are laid in groups of 30-50 on the underside of the foliage. After egg hatch, the tiny larvae begin feeding on the leaves. The larvae feed on the underside of leaves and actually skeletonize the foliage leaving only the upper surface in tact. Infested elm trees often have a brown or yellow appearance. If feeding is heavy, defoliation can be extensive. The larvae feed for about three weeks and then migrate down the trunk of infested trees. Gathering in large masses, they pupate or turn into adult beetles. This process takes about 1-2 weeks.

An examination of area elm trees found fully-grown larvae at the base of trees and in the process of pupating. At this stage, the larvae are resistant to insecticide applications. An area homeowner reported a solution of several tablespoons of soap in a gallon of water sprayed on the larva was effective in killing the clusters. Once adult beetles emerge, they will fly up into elm trees to mate and lay eggs for a second generation.

Normally, older, well established trees can survive heavy feeding, but young trees or trees already under stress may be sufficiently weakened leaving them vulnerable to attack by other secondary insects and disease. If control is needed, foliar insecticide sprays should be applied soon after the larvae hatch from eggs. Treatment before this time will not be effective. Keep trees healthy by watering regularly and fertilizing either this fall or early next spring.

Contact your local Extension unit office for the current chemical recommendations. Make sure to read and follow all label directions.

by  Editor, theCity1.com
May 21, 2007

 

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