Key symptoms

Dutch elm disease is a fatal fungus that can affect all elm species in Alberta. The fungus clogs the elm tree’s water conducting system and will cause the tree to die quite quickly, usually within one or 2 seasons.

  • Leaves on one or more branches suddenly wilt, droop and curl.
  • Leaves turn yellow, then brown and shrivel, but stay on the tree; this is referred to as “flagging”.
  • DED symptoms can also be seen under the bark of infected branches. When the bark is peeled back, healthy elm wood is cream-coloured. But when a tree is diseased, dark brown or red streaks can be seen in the infected sample.
  • DED advances quickly and the affected branch will die as more of the tree becomes infected. You might see dead leaves falling out of season.
  • If the tree is infected later in the summer, the leaves on the infected branch or branches will droop, turn yellow and drop prematurely. Late season infections are easily confused with normal seasonal changes in leaf color.

Two other diseases which are not as serious as DED (Verticillium wilt and Dothiorella wilt) can mimic the symptoms of DED so it is necessary to take a sample from the infected area of the tree to confirm if DED is present.

Figure 1. Early Symptoms – green, wilting leaves

Figure 1. Early Symptoms – green, wilting leaves
Source: Joseph OBrien, USDA Forest Service, Bugwood.org

Figure 2. Mid Summer – Clinging, brown, wilted leaves

Figure 2. Mid Summer – Clinging, brown, wilted leaves
Source: Minnesota Department of Natural Resources - FIA , Minnesota Department of Natural Resources, Bugwood.org

Figure 3. Tree showing flagging

Figure 3. Tree showing flagging
Source: Fred Baker, Utah State University, Bugwood.org

Figure 4. Tree showing flagging

Figure 4. Tree showing flagging
Source: Edward L. Barnard, Florida Department of Agriculture and Consumer Services, Bugwood.org

Figure 5. Staining of sapwood

Figure 5.  Staining of sapwood
Source: R. Scott Cameron, Advanced Forest Protection, Inc., Bugwood.org

Figure 6. Staining of sapwood

Figure 6.  Staining of sapwood
Source: George Hudler, Cornell University, Bugwood.org