Thursday, September 22, 2011

Bronze leaf disease reappears in Calgary

Some Calgary trees are at risk of being infected with bronze leaf disease (BLD). BLD is a relatively new disease in Calgary. It’s a fungus that infects various poplar species and hybrids; specifically Trembling Aspen, Swedish Columnar Aspen and Tower Poplar. BLD can kill an infected tree within three to five years of initial infection.  Early detection and treatment are important to save trees and prevent widespread infection.

The City has been in the process of identifying the scope of BLD in Calgary since 2010 and is monitoring, diagnosing and treating BLD in City-owned trees. The City does not have the capacity to monitor, diagnose and treat BLD in privately-owned trees, and is asking Calgarians to recognize symptoms and contact a local tree care professional for diagnoses and treatment options. 

BLD spreads from one tree to the next via airborne spores, which disperse in early spring.

  • Diseased leaves often first show up in the lower crown but may be scattered throughout the crown of the tree or isolated to a few branches.
  • Leaves become dark reddish-brown, chocolate brown or bronze although the veins and the leaf stem may remain green for some time.
  • Infected leaves remain on the tree through winter.
  • Once the disease spreads, browning may be observed under the bark of diseased branches.
  • New leaves on infected branches may appear underdeveloped in subsequent years.
Infected branches should be taken to a City of Calgary landfill for proper disposal. They should not be chipped, composted or used for firewood. For more information call 311 or go to

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