Cytospora canker of spruce

From Bugwoodwiki

U.S. Department of Agriculture, Forest Service. 1979. A guide to common insects and diseases of forest trees in the northeastern United States. Northeast. Area State and Private Forestry, Forest Insect and Disease Management., Broomall, PA. p. 123, illus.(USDA Forest Service, Northeast Area State and Private Forestry Publication. NA-FR-4)

Cytospora canker of spruce is caused by the fungus Cytospora kunzei. The fungus is found most frequently on Norway and blue spruces, but also attacks white spruce, red spruce, Koster's blue spruce, and Douglas-fir. Branch cankers disfigure the trees, but rarely kill them. Trunk cankers, however, sometimes girdle and kill the trees. Cytospora canker sometimes attacks young trees, but it is more common in trees15 years of age and older. Trees of low vigor, trees with shallow roots, those growing on unfavorable sites, and those weakened by drought, mechanical injury, or insects are more susceptible.

The first symptom of infection is usually the death of a lower branch and subsequent needle browning. As the disease progresses, infection spreads to higher branches. The cankers on infected branches are inconspicuous because the affected bark does not change color or become depressed. Infected areas may be covered by resin, which often drips onto lower branches. The removal of resin and outer bark from cankers reveals the brown, dead areas of inner bark and cambium.

Tiny, black, pinhead-like fruiting bodies of the fungus form in the areas of the bark where diseased tissue adjoins healthy tissue. During rainy weather, the threadlike, yellowish spore masses ooze from the fruiting bodies. The spores are spread by rain, wind, pruning tools, and possibly insects and birds. The spores infect through wounds.