Cause Cytospora kunzei (sexual: Valsa kunzei), a fungus that has not been reported in the Pacific Northwest but has been found by the OSU Plant Clinic. The disease is more common in the Northeastern United States. Rain splashes spores to wounded branches. The fungus infects through wounded tissue. Other species infect pine, Douglas-fir, and true firs. They also infect trees weakened by drought, fire, insects, and other diseases, most importantly dwarf mistletoe.
Symptoms Cankers start around bases of small twigs or trunks. Branches near the ground turn brown and die. More branches continue to die slowly up the tree. Occasionally high branches are attacked. The needles may drop right away or persist for a year. Eventually dry brittle twigs are left. White patches of pitch or resin may appear along the bark of dead or dying branches. Cankers are not readily seen unless the bark is cut back exposing the diseased tissue. Small black fruiting bodies (pycnidia) of the fungus may be seen in the cankered area.
Cultural control
- Remove and destroy infected branches.
- Avoid injuries to the bark from such things as lawn mowers and gardening equipment.
- Maintain healthy trees in the landscape through watering and fertility.
Reference Schoeneweiss, D.F. 1983. Drought predisposition to cytospora canker in blue spruce. Plant Disease 67:383-385.