Cytospora canker

Leucocytospora leucostoma (often identified as Cytospora leucostoma) is a destructive fungal pathogen responsible for Cytospora canker, a severe disease affecting stone fruit and pome fruit trees. It is classified within the Ascomycota phylum and is known for its ability to cause rapid decline and branch dieback in commercial orchards.

This pathogen specifically targets the vascular tissue and bark of trees like apricot, cherry, plum, and peach. The infection leads to the formation of cankers, where the bark becomes sunken, discolored, and eventually peels off. As the cankers grow, they can girdle branches or the main trunk, effectively cutting off the tree's water and nutrient supply.

The biological cycle of Leucocytospora leucostoma relies heavily on wound inoculation. Once inside the host, the mycelium colonizes the cambium layer. During wet conditions, the fungus produces pycnidia—small, flask-shaped structures—which release millions of spores that are easily spread by rain splashes or wind, leading to secondary infections on nearby healthy branches.

The fungus thrives in weakened trees, making environmental stress a major predisposing factor. Frost damage, sunscald, and improper pruning cuts provide the entry points for the spores. The pathogen is remarkably persistent and can remain active in dead wood for several years, making sanitation the most critical aspect of disease management in orchard environments.

Effective control measures include a rigorous sanitation program: pruning out infected limbs at least 15–20 cm below the visible canker and promptly removing dead wood from the orchard. Maintaining tree health through balanced fertilization and irrigation is essential to prevent stress-induced susceptibility. Additionally, applying copper-based fungicides during the dormant season can help reduce spore dispersal and minimize new infections.