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Dutch elm disease (DED) Ophiostoma ulmi and Ophistoma novo-ulmi

Gallery of European elm bark beetle showing the central main adult boring chamber and larval offshoot galleries, indicating the presence of elm bark beetle.
Example of curling, wilting leaves in the upper crown of a tree infected with DED.

Dutch elm disease (DED) is caused by a fungus, Ophiostoma ulmi (Buisman) and Ophiostoma novo-ulmi (Brasier), which blocks the tree's ability to conduct water and causes the tree to die.

The fungus is mainly spread by three species of elm bark beetles:

Other elm bark beetles and root grafts with neighbouring trees can also spread the disease.

Elm bark beetles are attracted to freshly pruned, sick, weak or dying elm trees. The larvae develop in the inner bark. Adults that emerge from infected trees will fly to healthy trees and infect them with the fungus, causing the disease to spread.

All species of North American elm are susceptible. The disease now occurs in most of the natural range of Ulmus americana from Manitoba to the Maritimes, with the exception of Newfoundland and Labrador. Saskatchewan is considered partially infested with Dutch elm disease.

Contact your local Canadian Food Inspection Agency office for additional information.

Popular links to provincial websites on Dutch elm disease

Elm pruning bans

Example of curling, wilting leaves in the upper crown of a tree infected with DED
Photo credit: R. McIntosh, Saskatchewan Ministry of Environment

It is illegal to prune elm trees in the following provinces during periods when elm bark beetles are active. Pruning the trees creates wounds that can attract the beetles and cause the disease to spread.

  • Alberta from April 1 to September 30
  • Saskatchewan from April 1 to August 31
  • Manitoba from April 1 to July 31

Elm species should not be pruned anywhere in Canada from April 1 to September 30 to reduce the risk of further spread within regulated and DED-free areas.

Winnipeg street before and after Dutch elm disease.
Photo courtesy of Alberta's Society to Prevent Dutch Elm Disease

What you can do

Example of "staining". Elm trees infected with Dutch elm disease may have red streaks through the sapwood.
Photo credit: R. McIntosh, Saskatchewan Ministry of Environment

What information is available?

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