It is still early to know the exact state of Lethbridge's Elm trees but City crews remain on high alert for European Elm Scale, an insect that threatened approximately two-thirds of the City's public elm population last year.
After an aggressive campaign to fend off the Elm Scale infestation in 2016, the City of Lethbridge continues to be diligent in the protection of the City's elm tree population. In mid-June of last year, City Council provided additional funding to treat approximately 3,600 public trees with TreeAzin, a natural insecticide, to combat European Elm Scale.
"How each tree responded to treatment appears to be quite different," says Kevin Jensen, Parks Operations Manager for the City of Lethbridge. "Some absorbed the TreeAzin well and it was carried throughout the whole tree. We are seeing very little Scale left in those trees. Other trees didn't have as good of an uptake. We saw this in trees that had lower moisture levels or damaged root systems."
Elm trees treated in 2016 will not be injected again this year as per the TreeAzin product recommendation. The process involves drilling and injecting into the trunk which, if done unnecessarily, could cause more damage to the tree.
City staff have been closely monitoring the trees through the spring and sending away samples to check the level of chemical left in the leaves. This helps determine when it would be appropriate to retreat the trees, should it be needed.
"In cleaning up broken branches from the thunder storm a couple of weeks ago, we have seen a reduction in Elm Scale which is a good sign. We do know that we still have a significant amount of Elm Scale out there and we want remind the public to be vigilant in caring for their own trees."
The City will continue to monitor public Elm trees and will implement a long-term rotating treatment schedule. It's estimated there are 11,000 elm trees in Lethbridge. Approximately 5,500 of them are on public property.
For more information on the signs and symptoms of Elm Scale and what you can do to protect your trees visit www.lethbridge.ca/elmscale. If an elm tree on your property is showing signs of stress from European Elm Scale, contact a qualified arborist who can administer a pesticide injection. If you have an elm tree on your boulevard that needs attention please, email firstname.lastname@example.org or call 403-320-3850.
Kevin Jensen | City of Lethbridge, Parks Operations Manager