Since about 2007 in the Calgary area there has been a new fungal disease, attacking Swedish columnar aspen, tower poplars and a few other poplar/aspen varieties, known as BLD or Bronze Leaf Disease (Apioplagiostoma populi). Bronze Leaf Disease is an airborne fungus that lives on trees and is spreads in the spring through infected debris and branches. This disease first shows up in the lower 2/3 of the tree. During leaf out in the spring the disease can be VERY hard to identify as the aspen leaves may look stunted and or weakened. However as the season progresses the edges of leaves on the infected branches will then begin to turn reddish or brown but the veins of the leaves will remain bright and colored. By midsummer the whole leaf will have turned dark in colour with the veins of the leaves still remaining coloured. By late summer the entire branch may look dark chocolate brown to bronze in colour and the leaves may even stay on throughout the winter. Left uncared for the tree can die in as little as 3 years while spreading the fungus to neighboring trees.
The Town of Chestermere is doing what we can to identify and prune any infected trees we have in our parks and boulevards. However our resources are limited and we are only able to monitor and maintain the trees on town property. This is where we need you the residents to help stop the spread. You can do this by monitoring and caring for the trees on your property as private trees will be the responsibility of property owners. If you are concerned that you may have Bronze leaf on your aspen or poplar trees contact a local tree care specialist as soon as possible, Bronze leaf can be hard to identify as there are a few other poplar and aspen diseases that have similar symptoms.
Bronze leaf can be controlled and maintained but once infected the tree cannot rid itself of the fungus as it moves systemically throughout the tree. BLD also cannot yet be chemically treated as there are no fungicides available yet for this disease. To control BLD you should promote tree health and prune out the infected branches a minimum of 20cm (8 inches) below the lowest visible sign of infection. Be sure to sanitize your tools after EVERY cut as infection may be spread by pruning with infected tools. Disinfection can be done by soaking your tools for a minute with a 10% bleach solution or 70% rubbing alcohol. Take all infected wood leaves and debris to the landfill to be disposed of. DO NOT use the clippings for mulch chip for ground cover or use for firewood as any of these actions may allow the disease to spread to new areas.
To find a list of ISA tree care professionals visit www.treesaregood.org
More information and images can be found on the City of Grande Prairie and Calgary websites.