Elm Leaf Beetle Location/Vulnerable Plants
The Elm Leaf Beetle is believed to have reached Baltimore from Europe about 1834. It is now enormously destructive throughout New England and the Middle Atlantic States, occurs scatteringly westward to the Mississippi, and is found on the Pacific Coast. It is confined to the elm, with Chinese and Siberian elms most severely injured.
Elm Leaf Beetle Appearance and Habits
The adult beetle is 1/4″ long, yellow, changing to olive with age, with black spots on the head and a black band on the outside of each elytrum or wing cover. It winters in protected places, often in houses, and in spring flies to the elm, where it lays a double row of yellow, lemon-shaped eggs on the underside of a leaf. These hatch in about a week into black-spotted larvae, which skeletonize the leaves, eating out everything except veins and epidermis. After 3 weeks of feeding, they crawl down the trunk and pupate at the base, more beetles appearing in 1 to 2 weeks, to eat holes through the leaf. There are two or three generations a year, with the elms either entirely defoliated or covered with crisp brown leaves. Two or three years of defoliation may mean death, and always mean a weakening of the tree so that it is subject to attack by the elm bark beetle, carrier of the spores causing Dutch elm disease.
How to Manage Elm Leaf Beetles
There are no proven methods of preventing the elm leaf beetle’s attack. Protect houses and garages, and keep the beetles from wintering inside, by caulking cracks. Monitor the elms to see if the damage is serious; if so, apply a narrow band of pesticide higher than human reach. A relatively harmless homemade pesticide of 3 ozs. laundry soap to 1 gal. of water will kill larvae coming down to pupate.