Cytospora canker is a fungal disease that affects a large number of tree varieties including spruce, willow, apple, birch, cottonwood, maples, peach, ash, honeylocust, silver maple and more. Many spruce tree varieties are particularly affected. The fungus establishes itself and grows in the bark of the trees or in the wood. Trees with root damage around construction areas and with branch damage due to storms or pruning are especially susceptible to cytospora canker infection. The disease kills branches or even the tree by girdling.
Symptoms: Visible cankers on trees and shrubs may be seen accompanied by dark patches of brown to black bark which becomes mushy and exudes an unpleasant odor. Liquid or sticky oozing may be seen on certain tree types. Dead twigs may be seen above the diseased parts.
More information: Colorado State University Extension, University of Minnesota Extension