This summer's aggressive campaign to fend off a European Elm Scale infection from more than 3,500 public elm trees is nearly complete.
Over the past eight weeks, more than 3,100 public elm trees have been injected with TreeAzin, a natural insecticide, to combat European Elm Scale, an insect that threatens approximately two-thirds of the city's public elm population. In mid-June, City Council provided additional funding for approximately 3,600 public trees to be treated this summer, rather than 600 as originally planned. The strategy is intended to address the majority of infected public trees.
"We've had some reports of honeydew excretions from these insects stopping within days of treatment, but that may also be coincidental with the insects' life cycle," says Kevin Jensen, Parks Operations Manager for the City of Lethbridge. "Insect numbers decrease only slightly during the first months after treatment. We should see significant decreases next spring."
The additional funding allowed external services to be contracted to supplement the efforts of City staff as well as the purchase of the additional quantities of TreeAzin required to do the job. Contractors have injected nearly 2,300 public elm trees, and City technicians have so far injected more than 800 public elms. Treatment of elms by urban forestry staff will continue until the trees are no longer actively absorbing the insecticide. Parks staff assessed public elm trees to identify those most in need of care.
"The total number of trees treated is slightly lower than originally anticipated due to larger-than-expected trunk diameters, which required additional doses of TreeAzin," Jensen says, adding that the quality of treatments performed by contractors was audited by certified arborists on staff with the City. "We also want to re-emphasize how important it is for residents to be aware and diligent in treating their own elm trees to help stop the spread. It's essential for property owners to help us in fighting European Elm Scale."
The City's elm tree plan going forward includes monitoring trees throughout the city, gathering and cataloguing photos and samples from infected trees, pressure washing small elm trees this fall after leaf drop, and developing a long-term rotating treatment schedule to maximize elm tree health in all areas of the city.
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, Parks Operations Manager
European Elm Scale is an insect that attacks a variety of elm trees by feeding on the sap. These insects feed on the trees and produce a large amount of honeydew (a sticky secretion) which eventually covers the leaves and bark in a black mold. Heavy infestation can kill weakened trees and cause branch dieback in healthy trees.
It's estimated there are 11,000 elm trees in Lethbridge. Approximately 5,500 of them are on public property.
European Elm Scale was first detected in Lethbridge in 2005. The Parks department was able to control the spread until a marked increase in 2012. A combination of factors over the last several years including warmer winters, hot dry summers and a lack of treatment product has now contributed to a serious infestation across the city.