By Joanne Steventon
Most trees have gone dormant for the winter, but some elms in the Ottawa area have shed their leaves and won’t be budding again next spring due to a fatal fungus ravaging this North American species.
Ed Lawrence, horticultural specialist for the National Capital Commission, says many of these magnificent trees that used to line Centretown streets are dying off as a result of Dutch elm disease.
This fungal disease is spread by the elm bark beetle, which Lawrence speculates made its way into Canada on a load of burl wood, (favored by woodworkers for it’s unusual grain patterns).
Diseased elm trees became visible in the Ottawa area in the early seventies.
This highly contagious fungus infects the xylem of the tree, which is the transportation system for nutrients and moisture to its extremities. Signs of infection are dried leaves and wilting limbs.
“The first thing you tend to see is curling of leaves at the tip of the crown,” says Lawrence.
David Barkley, program manager of forester field operations for the City of Ottawa, says the city has a current operating budget of approximately $15,000 a year to treat infected trees with a special fungicide.
Because it is an expensive treatment, Barkley says priority is given to larger trees in more prominent locations. He says one treatment for each of these trees, which are usually in the vicinity of 100 years old and 50 cm in diameter, costs between $100 and $200.
“It is very short-term and in order to keep up the protection, you have to do it on an annual basis,” says Barkley.
Barkley says that even though it’s not always 100 per cent successful, the treatment is still effective.
One elm that receives an annual dose of fungicide is located on Elgin Street by City Hall.
But Lawrence says many elms are still succumbing to the deadly effects of the disease.
“There are fewer and fewer elm trees around,” he says, noting the majority of elms you see today are young.
Lawrence says that because younger trees grow more vigorously, they are strong enough to fight off the disease. The growing process slows as they get older and the fungus can invade the tree much easier. Although it takes longer for the disease to conquer the larger, older trees, he says these are the ones that usually end up dying.
“They’re just not a long-term tree for us anymore.” However, Barkley points out that older elms are prime candidates for treatment because they usually take longer to fall victim to the fungus, which allows more time to spot symptoms before they die.
Another $15,000 has been set aside to care for trees not large enough to be considered for treatment.
Areas of trees that appear infected are removed, and those too far-gone with the disease are cut down.
Barkley estimates around 75 elms in the 20-25 cm diameter range have been removed this year.