See:
Peach (Prunus persica) - Cytospora Canker
Cause The OSU Plant Clinic has found Cytospora sp. on a few submitted oak samples since the 1950s. The fungus is opportunistic and is quick to attack plants predisposed by heat, drought, winter damage, or infection by other pathogens. It also can colonize dying or dead bark as a saprophyte. Overall, there have been no comprehensive and systematic studies on the canker pathogens of oak.
Symptoms Portions of the branch die and may develop small pimple-like fruiting bodies (pycnidia) of the fungus.
Cultural control
- Prune out and destroy affected limbs.
Reference Pan, M., Zhu, H., Liang, L., Tian, C. and Fan, X. 2021. Studies of canker and dieback of oak tree in China, with two Cytospora species described. Plant Pathology, 70:2005-2015.