See:
Poplar (Populus spp.) - Canker
Cause The fungus Encoelia pruinosa causes a very aggressive canker disease on mature trees and is relatively common in several aspen areas in Oregon and Washington. It is fairly common in aspen stands of the Blue and Wallowa Mountains. This canker is a problem after stand disturbance such as thinning or selective logging. Sooty-bark is also a problem in high-use campsite areas. Ascospores from infected or dead trees infect wounds any place on the trunk. Cankers enlarge quickly but trees do not form defensive ridges of callus. Once the bark falls off, numerous gray apothecia form in the blackened areas. When dry the apothecial cups curl up but open up when wet for a length of time.
Other canker diseases include Black, Cryptosphaeria, and Cytospora cankers. Cytospora commonly shows up as a secondary invader of the already dead tissue.
Symptoms Sunken elliptical areas first appear with blackened cambium. This blackened or sooty area remains on the tree even after the bark sloughs off. The sooty residue is often spotted in appearance on old cankered bark (sometimes referred to as leopard spotting). Cankers are at first 1 ft wide and 3 ft long but can later expand up to 12 ft long or more. Cankers are perennial and continue to expand each year around the tree trunk giving it a slightly zonal look. Canker margins do not look raised. Cankers on mature trees are often long with a spiral twisting along their length. Numerous gray dots, apothecia, appear within the blackened area. Mature trees can be girdled in a few years.
Cultural control
- Avoid wounding trees.
- Remove and destroy dead or severely cankered trees.
Reference Callan, B.E. 1998. Diseases of Populus in British Columbia: A Diagnostic Manual. Natural Resources Canada. Canadian Forest Service, Pacific Forestry Centre, Victoria, B.C. 157p.