Dutch Elm disease decimates Maritime forests
Urban tree populations continue to be eaten away by disease
William Wolfe-Wylie
CUP Atlantic Bureau Chief
SACKVILLE, NB (CUP) — A small beetle only three millimetres long has caused the death of tens of thousands of Elm trees across the Maritimes at a cost of hundreds of thousands of dollars to small communities. But while entire urban forests have been decimated, larger communities are promoting proven strategies in maintaining a canopy of greenery in urban environments.
There was a time when Elm trees made up as much as 60 per cent of urban tree populations. But since the introduction of Dutch Elm disease in North America in the mid-20th century, some communities are finding it hard just to keep up with removing the dead trees, let alone preventing further infection.
Truro, NS, a town of approximately 12,000 people, has, over the past two years, spent more than $200,000 on removing dead Elm trees and developing preventative systems.
But in Antigonish, NS, there is hardly an Elm to be found. “The problem’s gone now,” said Paul Chisholm, a horticulturalist at St. Francis-Xavier University. “Now it’s a dead issue.”
Chisholm said that there were once 75 Elm trees on the campus and that number has been reduced to two because of the disease.
Dutch Elm Disease is a fungal infection that attacks the Elm’s vascular system, the intricate veins and tubules that transport nutrients and water between the roots, leaves and other portions of the tree. The vector is a small beetle that jumps from tree to tree during the summer months and allows the fungus to spread, primarily through open wounds in the wood. Since a tree’s vascular system lies just below the bark, any wound provides open access for the fungus.
Two strains of the disease are known to exist and both can kill a tree in a very short amount of time. The slow strain can take as long as three years to kill a tree, but the quick strain can kill a tree in half that time from the point of infection.
According to Andrea Ward, Mt. Allison University grounds supervisor and certified arborist through the International Society of Arboriculture, the disease really hit Sackville two years ago and the university has been fighting the battle against the fungus ever since.
By pruning out infected portions of the tree in the winter, said Ward, they can prevent further infection in that tree by allowing the wounds to compartmentalize and seal themselves off from the outside world before the beetle becomes active again in the spring. Getting rid of the infected wood once it has been pruned out of the tree has also been key to preventing further infections.
There is also a new injection-based solution — Alamo, which is administered per tree per season and has effectively stopped infection in trees that have not yet been infected. But at a cost of approximately $300 or more per treatment per tree, it is prohibitively expensive for many small communities.
The City of Fredericton, NB, however, has taken a visibly proactive method to solve the problem. Fredericton’s once-prolific Elms have dwindled to 5 per cent of the total tree population, and it spends approximately 75 per cent of its arboreal resources on maintaining and protecting that Elm population.
In 1952, as the possible devastation that Dutch Elm disease could cause was first being realized, Fredericton formed the Tree Commission and engaged in an aggressive planting strategy to diversify its tree population in preparation for the onslaught of the disease. The result has been that while the Elm population was fading, more than 30,000 trees of a variety of other species were forming a new canopy over the city.
According to Don Murray with the Department of Parks, Trees and Playfields, Fredericton makes no effort to prevent infections. Citing the high cost of Alamo and the effectiveness of their current plan in maintaining Fredericton’s urban forest, he said there was little need.
“Our program was copied throughout Canada,” said Murray, noting that the program is one of the few effective ones that does not use chemicals.
The large-scale implications of Dutch Elm disease have proven to communities the dangers of monoculture planting in their urban environments. Literature has emerged and policies have been formed in a number of communities that promote strict diversity guidelines for all planting operations.
This way, said Ward, if a disease strikes one species of tree, the city’s forests will not “go from beautiful to nothing in a few years.”
