Bronze Leaf Disease

Deadly tree disease hitting Swedish aspen

Bronze Leaf Disease

Horticulturist Nikki Anguish prunes a tree infected with bronze leaf disease. Urban foresters are worried the fungus could attack native aspens, three million of which are in Weaselled Park in the SW.

City foresters worry fungus may infect Weaselhead

Homeowners should be on the lookout for a deadly tree fungus that has arrived in the city this year and targets a specific species of aspen, the city’s urban forester says.

Bronze leaf disease, which infects Swedish columnar aspen, has been found in a number of trees on city property, Russell Friesen said.

And while it’s a concern that the fungus, which untreated can kill a tree in less than five years, is now here, the bigger problem will be if it jumps to the more populous trembling aspens — three million of which grow in the Weaselhead alone.

“Our biggest concern is if this disease jumps from the Swedish to the trembling aspen,” Friesen said. “We haven’t found any in the Weaselhead. That’s our apocalyptic scenario, that it gets into the native aspens.”

So far, bronze leaf disease has been confirmed only in the Swedish columnar aspen, of which there are tens of thousands in the city. There are millions of the trembling aspen.

Friesen said the infected trees have been found in 10 neighbourhoods.

The city is monitoring city-owned land. It is asking homeowners to check their own trees and look for dark reddish-brown, dark brown or bronze coloured leaves, with very brown veins.

“We want to reduce the potential of infection,” Friesen said.

While the fungus attacks the trees in spring, it’s easiest to spot in fall, he said.

The infected leaves remain on the trees after the others have fallen or been blown away.

Friesen said pruning the affected branch to the tree trunk eliminates the problem, unless more than half the tree is infected. Then it must be removed.

Infected branches or trees should be taken to the city landfill — and not chipped, composted or used as firewood.

Most of the city trees have been handled by pruning, Friesen said, while about seven or eight have been removed.

“We’re going to be watching this and managing this for years to come,” he said.

The fungus spreads when spores are carried by wind or water.

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