Recent storms are increasing the risk of a deadly disease spreading among the tens of thousands of Edmonton’s elm trees. As the city continues to clean up broken tree branches and limbs from the storms that brought high winds and rain to the region, scientists warn that the smell of torn branches attracts bark beetles – spreaders of a fungus that causes Dutch elm disease. “Bark beetles respond to the volatiles that are produced by trees,” said Nadir Erbilgin, a professor and the chair of the Department of Renewable Resources at the University of Alberta. “If you cut some branches, I can guarantee you these trees will be attacked (because) they produce more chemicals than the trees nearby.” Since the disease was first reported in Edmonton two years ago, 14 cases of Dutch elm disease have been identified in trees in the provincial capital. Six of these cases are new this year: three have been reported in Rossdale, two in Glengarry and one in Northmount. Since it was first detected in North America in 1930, the disease has killed millions of elms across the continent. About 22 per cent of trees on city-owned land – 90,000 of them – are elms, with thousands more on private land. Mike Jenkins, a senior scientist with the City of Edmonton, says the city has one of the largest stands of Dutch elm disease-free elms in the world. He said elms were planted en masse across the prairies “as important parts of our urban forest infrastructure” and as shelter trees for farmhouses, the majority of Edmonton’s being American elms, which could pose a long-term problem when it comes to saving them. Siberian elms are another variety found across the Prairies. “We have very, very low genetic diversity in our elm population,” Jenkins told CTV News Edmonton on Tuesday. “If one tree is susceptible to the fungus or the beetle infestation, pretty much all of them will be. We’ve planted a nice monoculture smorgasbord along all of our boulevards.” The city suggests removing bark beetle habitat by pruning dead, dying or diseased elm tree branches between Oct. 1 and March 31, by disposing of elm wood immediately by burning it or taking it to the Edmonton Waste Management Centre and not combine elm wood with any other waste, including food scraps. Elms damaged by summer storms can be pruned but should have their branches chipped, burned or buried promptly, the city says. Written permission is needed to prune them during a ban period from April 1 to Sept. 30. The city maintains a webpage with more information on how to contain the disease’s spread. But one big advantage Edmonton has over other places that have seen elms wiped out – they’ve mostly disappeared from the eastern United States and Canada and are being greatly affected in Saskatoon and Winnipeg – is that there are no native elms in the city’s river valley. “We don’t have that corridor for the beetles to move through as a reservoir of unmaintained elms for it to develop in and spread out from there, so that’s been a huge bonus in our overall combating Dutch elm disease so far,” Jenkins said. “A lot of those advantages will disappear when we’re dealing with banded elm bark beetle, which can go into Siberian elms, which do tend to be less maintained. We don’t have as good a handle on exactly where all those populations are, and I think that’s a major part of why we’re seeing this resurgence of Dutch elm disease on the Prairies.” With files from CTV News Edmonton’s Noah Rishaug
