Cytospora canker of spruce
The most common and damaging disease of spruces used for ornament or windbreak in the Midwest is caused by the pathogenic fungus, Leucostoma (Cytospora) kunzei. In central Minnesota, blue spruce sustains the greatest damage when this fungus kills branches and causes profuse exudation of resin from branch and trunk cankers. Unsightly dead twigs and branches persist for many years, although attack usually does not begin until the spruce are at least l0 to l5 years old.
In landscape nurseries, small branches of young blue and white spruce may be attacked and killed. All kinds of wounds to the bark allow this fungus to enter the spruce tree and cause disease. Drought predisposes spruce to attack by this pest. Control includes removing infested branches, avoiding wounding, and watering during drought periods.