Elm Leaf Beetle

The elm leaf beetle is found wherever elm trees are growing. Although all elm species are subject to attack, the beetle prefers Chinese elms and American elms. Trees growing in urban locations are usually more heavily infested than those in forests.

The adult beetle is somewhat oval and about 114 inch long. When newly emerged from the pupa stage in the spring, the adult is light yellow with a black stripe along each outer margin of the back. As the beetles age, the yellow color dulls to an olive green. and the black stripes become less distinct. The eggs are bright yellow and spindle-shaped. They are laid in clusters ol'5-25 on the underside of elm leaves. New young larvae are black and slug-like. Full-grown larvae arc about 1/2 inch long, dull yellow with black head, legs and hairs, and a pair of black stripes along the back. The adult elm leaf beetle passes the winter in protective places, like under rough bark, in cracks and crevices or in buildings. It also overwinters in houses, particularly in attics. In many cases, adults may become a household nuisance in the fall when they go into hibernation and again in the spring when they attempt to leave the house. Starting about mid-May, overwintering beetles deposit their eggs on the underside of the leaves. These eggs hatch in about a week, and the larvae feed on the underside of the leaves for the next 2-3 weeks. Only the veins and upper surface are left, giving leaves a "skeletonized" appearance. The most heavily infested leaves turn brown as if scorched by fire. When full-grown, the larvae crawl down the trunk or drop to the ground and pupate at the base of the tree or in crevices in the bark. The adults emerge in about 10 days around July, feed again on the elm leaves and lay eggs for a second generation. These adults go into the hibernating stage for the next season. In our area there are usually two generations, but sometimes three will occur. First-generation insects are the most damaging. Beetles feeding will not generally kill an elm tree. However, severe feeding weakens a tree, making it more susceptible to attack by other insects and diseases. especially Dutch Elm disease. The elm leaf beetle does not carry this disease, but the elm bark beetle, which attacks weakened trees, does.

Cultural Practices for Control:
Proper tree care such as pruning and fertilization can help elms resist damage from elm leaf beetles. If elm leaf beetles are a yearly problem, insect control sprays may be the only good control method.

Pro Care Practices for Control:
Spraying to control elm leaf beetles should be timed to kill the young first-generation larvae and later the second-generation larvae. Trees with past damage should have yearly fall fertilization to help keep the tree healthy. Pro Care tree care can help control elm leaf beetles with a regular spraying and fertilization program.

The Pro Care staff is always ready to assist you with your trees and shrubs. Please call if we may provide any information to enhance your landscape's health or appearance.