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Symptoms and Signs

Dutch elm disease is a vascular wilt disease. The earliest external symptoms of infection are often yellowing and wilting (flagging) of leaves on individual branches (Figure 3). These leaves often turn brown and curl up as the branches die, and eventually the leaves may drop off. Although initially only a part of the tree crown may be affected, symptoms may progress rapidly throughout the crown. Highly susceptible trees often die in a single year, but others may linger for several years. Symptoms progress quickly and death may occur rapidly in trees infected in early spring, while trees infected later in the summer may survive longer.


Figure 3	Figure 4

If the bark of infected elm twigs or branches is peeled back, brown discoloration is seen in the outer layer of wood. This discoloration in the xylem actually occurs before the foliar symptoms described above are seen; foliar symptoms result when sap flow ceases in the infected wood. Xylem browning is often discontinuous. In cross section, it appears as a circle of brown dots or a ring (Figure 4). Other wilt diseases of elm, such as Verticillium wilt, also cause sapwood discoloration, so positive diagnosis of Dutch elm disease depends on laboratory culturing and identification of the fungus.

The signs (fungal structures) of the Dutch elm disease pathogens are found within infected elm trees, and are described in the Pathogen Biology section.

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