Mountain Ash (Sorbus spp.)-Cytospora Canker


Cause Cytospora chrysosperma (formerly Valsa sordida) has been reported from Washington and C. leucostoma and C. massariana (formerly Leucostoma persoonii, and L. massariana) are fungi that have been reported from Idaho. The OSU Plant Clinic also has found the disease on many plant specimens sent in over the years.

Symptoms Branch dieback of smaller twigs and cankers of larger limbs. Cankers can occur on twigs or large limbs. Cankers generally have a branch stub in the center. Vascular necrosis, cracking, splitting and discoloration of the bark occurs with cankers. Small bumpy fruiting bodies (pycnidia) of the fungus may be seen within the bark of the cankered area. Branch dieback symptoms can occur anytime of the year while cankers generally occur during the dormant season.

Cultural control

  • Avoid injuring trees during the growing season.
  • Provide water and fertilizer as needed for optimum growth.
  • Remove and destroy branches below the cankered area as they are discovered.

Reference MacBrayne, C.G. 1981. Canker and dieback of Sorbus spp. European Journal of Forest Pathology 11:325-333.