Larger Elm Leaf Beetle

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Elms have lots of pests. This week I have had several reports of larger elm leaf beetles, Monocesta coryli, infesting elms around Raleigh. I have not been able to find a specimen to get pictures. The pictures sent in by others show severe defoliation of even large elms.

Larvae of the larger elm leaf beetle. Photo: Gerald J. Lenhard, Louiana State Univ, Bugwood.org

Larvae of the larger elm leaf beetle. Photo: Gerald J. Lenhard, Louiana State Univ, Bugwood.org

Larger elm leaf beetles have one generation per year. Adults are active in spring and early summer laying clusters of eggs. Larvae feed all summer skeletonizing leaves in a fashion similar to other leaf beetles. In late summer (now) the last instar larvae are very large, around ¾ inch, and feeding heavily.

The larvae crawl down tree trunks to pupae and spend the winter in soil. One strategy for isolated elms is to spray the base of the trunk with a contact insecticide so larvae die on the way down. If other elms are nearby though this will not help much as the beetles move around a lot. Systemic insecticides can be applied by drench in early spring if trees are repeatedly infested. Find insecticides for leaf beetles in the 2017 Southeastern US Pest Control Guide for Nursery Crops and Landscape Plantings.