What is it?
Dothiorella elm wilt is a disease involving a fungus (Dothiorella ulmi) that causes the wilting and progressive die-back of American and Siberian elm trees. Symptoms of the disease are:
- Wilting, drooping, curling and yellowing of leaves, branch dieback, and browning of sapwood.
- Evident soon after leaf out and brown leaves persist on dead branches throughout the fall and winter.
- Impossible to visually distinguish from Dutch elm disease (DED).
What's the problem?
The disease attacks elms under extreme stress, a condition that impairs the trees' defences. Extensive annual surveying for the disease since 1996 has led to the discovery of hundreds of cases and many removals of American elm trees in Edmonton.
What can I do?
Prevention of Dothiorella wilt starts by keeping elm trees healthy. Watering trees during periods of drought will help lower their stress levels and increase their resistance to infection. Anti-fungal treatments so far have not proven effective in combating Dothiorella elm wilt in Edmonton.
Elms with recognizable wilting or die-back are declared "hazard" trees under Edmonton's Community Standards Bylaw #14600. A pink and black striped ribbon and a hazard tree tag on the trunk identify the tree as being diseased.
This action removes the tree from regular pruning activities, thereby reducing the risk of disease spread to healthy trees.
If you suspect that your untagged elm tree has Dothiorella wilt, please report it by calling 311 or emailing firstname.lastname@example.org. City personnel will assess your tree and take samples of branches that show signs of fungal infection for testing at the University of Alberta's plant pathology laboratory.
Unlike Dutch elm disease, Dothiorella wilt requires no insect or other organism to spread the disease. Studies elsewhere have shown that Dothiorella fungus is spread as microscopic spores by water or wind.
The disease begins in weakened elms when spores enter natural wounds, cracks, pruning wounds or tiny pores in the bark called lenticels.
Infected elm trees that exhibit extensive canopy die-back are removed and replaced with non-elm species to promote diversification of the urban forest.
To reduce the spread of the disease, any wood removed from a hazard tree or stump must also be disposed of at the Edmonton Waste Management Centre where it will be converted to compost.