Cytospora canker

Cytospora canker, caused by the fungal pathogen Cytospora leucostoma, is a common and destructive disease affecting the bark of numerous trees. It typically manifests as necrotic lesions that disrupt the transport of water and nutrients, eventually leading to branch dieback.

A wide range of woody species serves as hosts for this fungus. Among the most susceptible are stone fruits such as common apricot, common cherry, sour cherry, and peach. Additionally, the pathogen impacts nut-bearing trees like hazelnut (filbert), ornamental species such as elm and plane trees, and conifers like the Douglas fir.

Symptoms typically involve the development of sunken or swollen areas on the bark. As the disease progresses, the bark may crack, and small, raised fungal fruiting bodies (pycnidia) appear. Under moist conditions, these structures release spores that spread through wind, rain, or human activities.

The development of the disease is highly dependent on environmental stress factors. Drought, winter injury, sunscald, and improper pruning cuts create favorable conditions for the fungus to colonize the tree. Once established, the mycelium spreads within the bark, effectively girdling the stem or limb.

Effective management relies primarily on cultural practices, as there is no single chemical cure. Key strategies include pruning out and destroying all infected wood, ensuring trees remain well-hydrated and fertilized, and protecting trunks from sunscald. Prompt removal of dead or declining branches is crucial to reducing the local inoculum load.