Bronze Leaf Disease

What Trees Does This Disease Affect?
Swedish Columnar Aspen, tower poplar, poplar hybrid clones

What is the Disease Cycle?

Spores are released from mature preithecia (spore producing structures that develop on overwintered leaves). The spores are then spread during the spring to infect leaves on the same tree and other nearby trees. The disease will develop over the summer and infections will spread internally to other parts of the trees. Symptoms typically appear in later summer (early-mid August) or early fall (September). You will begin to see individual branches or a few leaves suddenly show symptoms.
Bronze Leaf Disease
What Conditions Help Spread the Disease?
Rain and moderate to warm temperatures (18 degrees Celsius) lead to spore dispersal.

What Are the Symptoms?
Leaf tissues turn orange-brown to reddish-brown, starting from the edges of the leaf, moving inward towards the base of the leaf. Leaf veins and petiole remain a bright green colour. All leaves on a branch may be affected. Discolouration deepens to a bronzy, reddish-brown colour as the season progresses.

Infected leaves will often remain attached to the tree over the course of the winter (they do not fall off). Branches may dieback as the disease progresses systemically. Leaves that overwinter may have a pebbly surface texture (like the surface of a curling rink), reflecting the development of spore-producing structures (perithecia).
Tree with visible damage from bronze leaf disease
What Can You Do?
Prune affected areas of the tree. Cut off leaves and branches, place in a sealed garbage bag and dispose of in your black waste cart or take to the landfill. The sealed plastic bag will help prevent spores from spreading the disease.

Please do not burn, compost or dispose at a recycle centre. Monitor your trees and prune out any infected branches. If trees are heavily infected it is best to remove the entire tree.