What it is?
Dutch Elm Disease (DED) is a devastating disease that affects all elm species. It is caused by a fungus primarily spread by three species of elm bark beetles. The disease obstructs the tree’s ability to transport water, ultimately leading to its death.
Alberta was free from Dutch Elm Disease for the past decades. However, Edmonton confirmed dutch elm disease in August 2024. Calgary is still free from disease as of today(Jan 2026). This disease can cause disastrous consequences if left alone.
Symptoms
- Wilt or droop leaves in tree canopy in summer time, and remain attached to the tree in the winter
- Red staining in the sapwood if peeling off the bark of infested parts.
- Beetle emergence holes with distinctive breeding gallery pattern under the bark.
Damages
- The beetles will breed in weak and dying trees, carrying the disease and than fly to healthy elm to feed.
- Dutch elm disease can kill elm tree within 1 to 2 seasons.
- In 1970s, nearly 90% of elm trees are killed in Montreal, 80% of elm trees are killed in Toronto.
What to do?
- Keep your elm tree healthy.
- Strictly follow the elm pruning ban to prevent DED. Only pruning elm trees between April 1 and September 30 in Alberta.
- Check your elms for signs of DED periodically and report any suspected signs of the disease or the beetle to the City.
- Don’t transport or store elm firewood.
Other resources:
https://tidcf.nrcan.gc.ca/en/diseases-caused-by-pathogens/factsheet/10
https://inspection.canada.ca/en/plant-health/invasive-species/plant-diseases/dutch-elm-disease