Issue 4, May 18, 2015

Elm Leaf Beetle

Elm leaf beetle larvae are present in southern and central Illinois. This pest is less common in northern Illinois but larvae should be present by the end of the month. These larvae can be serious leaf skeletonizers of elm and zelkova. In general, European elms are attacked heaviest including Siberian (Ulmus pumila), English (U. procera), and "urban" (U. pumila X U. hollandica X U. carpinifolia) elms. Chinese elm (U. parvifolia) is usually only lightly damaged, with American elm (U. americana) feeding damage intermediate between Chinese and European species.

Young larvae are gray to black and window feed by eating the leaf's lower surface and interior, leaving the upper surface intact. Although this window feeding is initially clear to whitish, the exposed cells die and turn brown. Heavily attacked trees are covered with brown leaves. Mature larvae are about ¼ inch long. They are yellow with a black lateral stripe on each side. Large larvae skeletonize the leaves. Fully grown larvae form bright yellow pupae in bark crevices and at the base of the tree.

Elm leaf beetle larvae and damage.

Adult beetles are about ¼ inch long. They are yellow with black lines down the middle of the back and along each side. They eat roundish holes in the leaves; heavy infestations defoliate trees through skeletonizing the leaves. Adults lay ¼ inch long oblong masses of yellow eggs on the leaf undersides. There are two to three generations per year, with three generations in southern Illinois. Adults overwinter under loose bark. Overwintered adults have a dull appearance as the bright yellow of the newly emerged adult turns an olive green over the winter.

Elm leaf beetle adult and damage.

Insecticidal soap can be used to control young larvae, but is not as effective against older larvae. Acephate (Orthene), carbaryl, (Sevin), imidacloprid (Merit), lambda-cyhalothrin (Scimitar, Demand), and spinosad (Conserve) are effective as sprays against all larval stages and adults. Imidacloprid is also effective as a soil drench or injection. (Phil Nixon)

Phil Nixon

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