See:
Poplar (Populus spp.) - Canker
Cause Cytospora chrysosperma has been reported from all three Pacific Northwest states. This disease is widespread and common on poplar, cottonwood, aspen, and willow; occasionally on mountain ash, maple, and cherry. Although the disease is found on many hosts, the fungi responsible may be host specific. Isolates from aspen or cottonwood were not pathogenic on alder, ash, elm or willow but were able to infect each other. The fungus is generally considered weakly parasitic entering through wounds that may be due to frost, sunscald, heat and drought stress, insect damage or browsing damage by elk, deer, or domestic livestock. Weakened trees are more susceptible.
Other canker diseases include Black, Cryptosphaeria, and sooty-bark cankers.
Symptoms Young twigs develop brownish, sunken, roughly circular areas in the bark. The fungus may grow down the twig and into larger branches on the trunk. Large cankers may be on branches and trunks. Infected bark discolors to orange or orange-brown and eventually darkens to black. This orange-brown bark discoloration is the most common and easily observed symptom and is frequently accompanied by an orange-brown liquid ooze. Pycnidia in the bark give the canker surface a pimpled appearance. Later, a perithecial stroma develops in the dead, cankered areas. Twigs and smaller branches may die back without definite cankers. Cankers may enlarge over time, killing the tree or predisposing it to damage by other agents including wind.
Cultural control
- Keep trees in good vigor and avoid wounding.
- Conifer control will help reduce moisture stress and increase sunlight. Do not injure aspen when conifers are removed.
- Minimize livestock browsing with fencing. Conifer slash left within an aspen grove can also help deter cattle from grazing.
- Remove and destroy dead or severely cankered branches.
References Bates, J., Davies, K., Deboodt, T., Fitzgerald, S., Humphrey, A. Kaiser, J., Lowrie, J. Markus, A., Rodhouse, T., Sharp, R., Stringer, D., and Strong, N. 2010. Land Manager's Guide to Aspen Management in Oregon. OSU Extension Service. EM 005.
Kepley, J.B. and Jacobi, W.R. 2000. Pathogenicity of Cytospora fungi on six hardwood species. Journal of Arboriculture 26:326-332.