Dutch elm disease (DED) is a fungus that has decimated the native elm tree population in North America. The fungus moves through root-to-root contact of similar elm species or is carried by bark beetles from infected trees to other elm trees. Fresh wounds inflicted in the growing season are very attractive entry points for these beetles. This disease kills the tree, causing leaves to wilt, curl, yellow and eventually drop.
The City of Toronto monitors City-owned elm trees over 30 cm in diameter from June to early October for symptoms of DED.
Where appropriate forestry crews may prune diseased City-owned elm trees from October to May. Removals however, can occur at any time of year once a tree is heavily infected.
The City will also inject a fungicide into significant, species-susceptible City-owned elm trees that do not show symptoms of DED. Arbotect 20-S is the fungicide that is used for the treatment. Protection to the tree lasts 3 years, is meant to be preventative but does not guarantee the tree will not get DED.
For more information, please visit the City of Toronto website.