Dutch Elm Disease
Dutch Elm Disease (DED) is a devastating disease that can affect any type of elm tree. The disease has destroyed millions of trees in North America since being introduced from Europe and is prevalent in Manitoba, Saskatchewan and Montana. Fortunately, Alberta has been able to remain DED-free and has the largest disease free American elm stands in the world.
Elm trees are easy to identify. They have tall, straight trunks with thick, rough bark that is grey or greyish brown. Branches flare out at the top to form an arch or umbrella, providing lots of shade. The leaves are about 4 inches long and have a double-toothed edge.
The disease is caused by a fungus which is spread by several species of beetle, including the native elm bark beetle and the European elm bark beetle. These beetles are very small, but can create enormous damage to elm trees and elm populations. Look for beetle emergence holes, which will be about the size of a pencil lead, and sawdust on the bark. This can be an indication of beetle activity in elm trees.
European Elm Bark Beetle (Left) and Native Elm Bark Beetle (Right)
Trees infected with DED generally show flagging, which means the leaves of a single branch will turn yellow and begin to wilt, and then turn brown and die. The leaves will remain on the tree. The wood below the bark of infected branches will show a brown staining caused by the fungus.
Flagging caused by DED and Staining caused by DED - left and middle branches are affected
What can you do to prevent DED?
There are several things that you can do to help prevent the spread of DED and protect your elm trees. There are nearly 5000 elm trees within the boundaries of our municipality, so it is important that we protect these trees and prevent the spread of this disease.
- Keep your trees healthy. Elm trees should be well watered from April to mid-August. Trees should not be watered after mid-August, but they should get a good soaking a few days before freeze-up.
- Dead branches and trees should be removed to eliminate possible beetle habitat. There is a mandatory elm pruning ban from April 1 to September 30. Beetles are active during this time and are attracted to the scent of freshly cut wood. Dead branches should only be pruned from October 1 to March 31.
- Dispose of all elm wood by burning or chipping. Do not store elm firewood. Do not transport firewood into Alberta. If elm wood is chipped, the chips should be no larger than 1 inch.