Dutch Elm Disease

Dutch Elm Disease (DED) is caused by the fungi Ophiostoma ulmi and Ophiostoma novo-ulmi. These fungi develop in the the vascular tissue of the tree. In response, the tree produces small gum blobs that stop the growth of the fungus but also cut off the sap flow in the vascular tissue. Branches die as a result, after which the entire tree dies. Dutch Elm Disease is found in Europe, North America, Canada and New Zealand.
The fungi are spread by the small and large elm bark beetle (Scolytus scolytus and S. multistriatus) and by root contact between trees standing together.
The beetle feed on the axillary buds of trees, infecting the tree with fungi. Once the trees are weakened by fungus, the beetles lay eggs in a tunnel under the bark.
Dutch elm disease is highly contagious. Moved Infected dead wood provides a new source of infection.