Cytospora canker of willow

The disease is caused by the fungus Cytospora pruinosa, a pathogenic ascomycete responsible for bark necrosis and canker formation. It primarily targets the vascular system and cambium, disrupting nutrient and water transport within the affected branches or stems.

The main host plants are willow species (Salix). Susceptibility to the infection is significantly higher in stressed, drought-stricken, or wounded trees, as well as in specimens planted in non-native or unfavorable urban environments.

Symptoms of the infection include the appearance of depressed, discolored lesions on the bark, which later turn brown or dark grey. Under suitable conditions, the fungus produces pycnidia, appearing as small pimple-like bumps on the bark. During wet weather, these structures exude characteristic orange or yellowish tendrils of fungal spores.

The spread of the disease is highly dependent on environmental stress factors, including winter sunscald, frost cracks, and pest infestations. The fungus enters the plant through these physical injuries, and high ambient humidity facilitates the rapid germination and colonization of the bark tissue by the pathogen.

Management strategies focus on preventive measures, including regular sanitation pruning to remove infected limbs well below the visible margin of the canker. It is crucial to maintain tree vigor through proper irrigation and fertilization, while ensuring that all tools are disinfected to prevent the spread of spores during maintenance operations.