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Bronze Leaf Disease of Poplar and Aspen | |
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From the Apr 27, 2009 Issue of Agri-News | |
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"If you were to go outside for a walk almost anywhere in Alberta, you wouldn't have to go far to find a poplar or aspen tree," says Robert Spencer, irrigated and specialty crops specialist with Alberta Agriculture and Rural Development, Stettler. "One of the most popular and best-selling tree species in Alberta is the Swedish Columnar Aspen. It is valued for its narrow, tall growth habit and rapid growth rate, but it's also one of the aspen species susceptible to BLD."
Over the past few years, Alberta Agriculture and Rural Development staff members, led by Dr. Ron Howard, have conducted a survey project to determine if and where this disease is present in Alberta. Nurseries and municipalities across the province have participated and assisted in survey activities. The survey produced a number of presumptive positive samples that were collected from several municipalities.
"Symptoms of BLD typically appear in mid-August," says Spencer. "Infected leaves turn a reddish-brown colour from the leaf margins (edge) in towards the leaf base, with the whole leaf eventually turning colour. The leaf veins and petiole (leaf stem) may remain green for a time. All or a few leaves on a branch may be affected. The reddish-brown or bronze colour can become darker as the season progresses. Infected leaves often remain on the tree throughout the winter.
BLD is initially introduced by spores, but moves systemically within the branch, eventually causing the death of the affected tree. The rate of death can vary, but trees may die within three to five years."
BLD cannot be controlled by chemicals. It can only be managed by ensuring good sanitation practices (removing leaves, pruning out diseased material) and maintaining good plant health and vigour (adequate water, fertility, etc.). Diseased material should be pruned out below the lowest visible point of infection. Trees that are so severely infected that pruning is impractical, or trees that have recently died from BLD, should be removed, burned and/or buried to reduce the risk of disease spread.
The challenge with this disease is that positive identification of the disease cannot be based solely on visual symptoms. Diagnosis is typically accomplished by examining the fruiting bodies of the causal pathogen; however, this is difficult because the fungal fruiting bodies only form after an over wintering period. Infected, over wintered leaves with fruiting bodies often have a "bumply" texture to the leaf (similar to the pebbled texture of a curling rink surface).
To overcome some of the difficulties of diagnosis, a molecular test was developed by researchers at the Agriculture and Agri-Food Canada Research Centre in Lethbridge, which allows quick and accurate determination of BLD infection. Preliminary test results on material collected from central and southern Alberta in 2007 suggest that BLD was present in some of these samples.
Contact:
Robert Spencer
310-FARM (3276)
The contents of this page are no longer available.
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For more information about the content of this document, contact Robert Spencer.
This document is maintained by Rita Splawinski.
This information published to the web on April 22, 2009.
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