Cytospora Canker on Spruce

Cankers, sunken dead areas of bark and underlying wood, form on the lower branches of the trees, girdling small branches in one or two years and large branches after several years. Resin flows out of the cankers and may drip down on lower branches.

Cytospora can infect branches through wounds and branch stubs, but does not actively develop a canker unless the tree is stressed by drought. Small fungal structures, in which thousands of spores form, develop in the canker. However, during wet weather, the spores ooze out in long yellowish threads. Rain splashes the spores onto other branches, and the branch killing proceeds up the tree.

Management

Since the fungus readily infects wounded tissue but remains latent in the tree without causing symptoms, fungicide sprays cannot be effectively timed to prevent this disease.

Select the planting site carefully, avoiding drought-prone sites. Anticipate the future needs of the mature tree and consider whether the site has the potential to supply the water requirements of a 50-60-foot tall specimen.

Prune infected branches, disinfesting the tools between cuts.

References

• Blanchard, R. O. and T. A. Tattar. 1981. Field and laboratory guide to tree pathology. Academic Press. New York. 285 pp.
• Schoeneweiss, D. F. 1983. Drought predisposition to Cytospora canker in blue spruce. Plant Disease 67:383-385.

Prepared by Gary W. Moorman, Professor Emeritus of Plant Pathology