Bronze Leaf Disease - Frequently Asked Questions

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 Bronze Leaf Disease (BLD), caused by the fungus Apioplagiostoma populi, is a disease affecting Poplars, primarily Swedish Columnar Aspen, 'Tower' poplar and poplar hybrid clones. We've received a number of calls about this disease so here are some of the more frequently asked questions.

What is the life cycle of the disease?
In the spring, mature perithecia (spore-producing structures found on overwintered leaves) release spores which is hastened by rain and warm temperatures. These spores wash/blow to other leaves on the same tree or trees in the vicinity and the disease develops over the summer. Once leaves are infected, the disease can then be spread throughout the tree (systemically) or via spores. Due to how poplars are often propagated by vegetative cuttings, the disease can also be spread by these cuttings. Once infected, without proper management, a tree can die within 3-5 years.

What are the symptoms?
Typically symptoms appear in later summer (early-mid August) or early fall (September) and may be relegated to only a few branches or leaves. Symptoms may spread around the tree and dieback may occur on infected branches. Infected leaves turn orange-brown to reddish-brown and typically colouration starts at the edges of the leaf and moves inward toward the base. A defining characteristic of the disease is the way that the leaf veins and petiole often remain a bright green in stark contrast to the rest of the leaf.

Affected leaves will often remain attached to the tree throughout the winter and in spring, may appear to have a bumpy or pebbly surface caused by the development of perithecia.

Bronze Leaf Disease on Swedish Columnar Aspen
Distinctive foliar symptom on Swedish Columnar Aspen
Photos by Rob Spencer
Infected leaves
Progression of colouring on Swedish Columnar Aspen leaf
Photos by Dustin Morton

What can BLD be confused with?
Bronze Leaf Disease can sometimes be confused with spring colouring in new growth leaves. Stress, be it moisture, heat or otherwise, can also cause colouration in hybrid poplars which may be confused with BLD. In the fall, the disease can also be confused with fall colouration. The symptoms mentioned above can be used to help differentiate both of these from BLD.

Can I spray something to fix my tree?
No, there are no registered chemicals for BLD.

What can I do to save my tree?
Good sanitation is the best method of controlling the disease. Prune out affected branches 20-30 cm (8-12 in.) into healthy wood while still attempting to maintain the tree's shape. Often in these trees, this is back to the trunk. Pruned wood should be bagged and disposed of in the garbage or burned immediately. Removal of dead and or dying trees is important as they will infect nearby trees as well. Chipping or composting infected wood will only help to spread the disease and should be avoided.

Equipment used to prune trees should be sanitized between cuts to avoid transferring the disease. A simple solution can be made out of 1 part household bleach and 3 parts water. Tools should be allowed to soak for 5 minutes in the disinfectant and rinsed with clean water before being used again.

Avoid planting susceptible tree species in areas where the disease is present. Further attention should be paid to how close together trees are planted as increased air flow and reduced humidity will decrease the incidence of disease. Ensure there is air movement through the trees canopy as well by maintaining good pruning practices.

As with all tree diseases, the best defence is a healthy tree. Ensure that your trees are well pruned, well watered and fertilized appropriately.

Should I report an infected tree?
Some cities and/or counties track infections of BLD. Contacting your local municipal government is recommended.
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For more information about the content of this document, contact Robert Spencer.
This information published to the web on August 26, 2014.
Last Reviewed/Revised on October 16, 2014.