University of Manitoba - Faculty of Agricultural & Food Sciences - Bronze Leaf Disease of Poplar
Bronze Leaf Disease of Poplar

Problem type: Disease

Name of problem: Bronze leaf disease of poplar

Plant name(s): Poplar/aspen, especially Tower poplar and Swedish Columnar aspen

Symptoms / Characteristics:

In midsummer, leaves turn reddish-brown, beginning at the leaf edges and moving inward. Symptomatic leaves typically originate in the lower crown and eventually spread throughout the entire canopy. Discoloration may be observed as single leaves or entire branches. The interior tissue of infected branches and stems may also be bronze-colored. Leaf stems and veins often remain green. By late summer, the dark reddish-brown or bronze leaves dry up and curl inward. Infected leaves may remain on the tree until spring. The leaves of infected trees are underdeveloped and heavy infestation can lead to branch dieback.

Bronze leaf disease diagnosis may be difficult because several other poplar diseases have similar symptoms and not all species and varieties of poplar exhibit the same symptoms. Leaf reddening rather than browning, and green veins rather then brown help to distinguish this disease from Venturia leaf blight of poplar. Symptomatic leaves associated with septoria leaf spot of poplar may also resemble those associated with bronze leaf disease. However, septoria infected leaves tend to be more spotted and these spots often have centers, giving them a bulls-eye appearance

Control / Preventions:
The fungus that causes bronze leaf disease of poplar, Apioplagiostoma populi, moves systemically (within the plant's vascular system), therefore, once established it cannot be removed. Begin inspecting host trees in spring when the leaves are beginning to emerge. New leaves of an infected tree will likely be chlorotic (yellowish) and will exhibit symptoms of bronze leaf disease rather quickly. Remove infected branches once the disease has been confirmed. The entire removal of heavily infested trees may be necessary. In the fall, collect and discard all fallen leaves in order to reduce potential overwintering of the fungus. The most susceptible species of poplar and aspen should not be used in shelterbelts or other mass plantings, as this promotes rapid spread of the disease. To date, there is no registered chemical control for bronze leaf disease of poplar.

This factsheet is adapted from MAFRI (Manitoba Agriculture, Food and Rural Initiatives)