Seiridium Canker

Seiridium canker shows up as branch dieback and stem cankers on Port Orford cedar, incense cedar, and arborvitae. You'll see discoloration and sunken areas on branches and the main stem, often starting on lower growth and gradually progressing upward. The cankers may weep or show resin bleeding. Look for this disease year-round in Western Washington, but infection pressure is highest during wet periods when wounds are most susceptible to invasion.

This disease can weaken or kill valuable ornamental conifers, particularly mature specimens that have been stressed by drought or poor site conditions. The key to managing seiridium canker is prevention through proper cultural practices: maintain tree vigor with appropriate irrigation and drainage, prune out infected branches as soon as you notice them, and avoid wounding trees during wet weather when spores are most active.