University of Maryland Extension

Dutch Elm Disease - Trees

dutch elm disease symptoms

Photo: Dutch elm disease. Symptoms typically appear in May as wilted branches that show yellow then brown leaves

Back to Common Problems - Trees and Shrubs

dutch elm diseaseDutch elm disease is a serious lethal disease that infects a large number of elm species including American, winged, slippery, rock, and September elms. Symptoms typically appear in May as wilted branches that show yellow, then brown, leaves. Dried leaves may remain attached to the branches or may fall, leaving bare twigs. As symptoms progress, entire limbs may show wilt symptoms and once infection reaches the trunk the entire tree may wilt. In older trees wilt symptoms may progress throughout the canopy for several years before death occurs. Infected twigs and branches typically show vascular streaking under the bark.

Photo: American elm tree showing typical flagging and dieback symptoms due to Dutch elm disease. C. Kaiser, U. of KY, Bugwood.org


beetle feedingThis fungal disease enters through feeding wounds made by the native elm bark beetle and the more prevalent, smaller, European elm bark beetle (see photo). Beetles breed beneath the bark of dying or recently dead elms. Infected or stressed trees actually emit an odor that attracts beetles to them for breeding and egg laying. In addition, female beetles also emit attractants that lure additional beetles to declining trees. There are up to three generations a year with the first emergence starting in April from overwintering larvae. Beetles that emerge from infected trees typically are covered with fungal spores growing in the pupal chambers. Beetles flying to other trees spread the spores to other trees.

Management strategies: The chief strategy for control of Dutch elm disease is thorough early removal of newly infected branches to interrupt the spread by elm bark beetles. Ideally, removal should occur within two to three weeks after symptoms appear during the growing season. Diseased wood should be chipped and removed from the site. Pruning cuts should be made at a branch fork at least 10 feet below visible streaking in the sapwood. Pruning will be most effective if less than five percent of the crown is affected. High-value trees may be appropriately injected with systemic fungicides. This is expensive and may need to be repeated in one to three seasons. If injections will be used, prune after the injections are complete.

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