Corinectria tsugae

Corinectria tsugae is a fungal pathogen known for causing bark necrosis and canker-like symptoms on various species of hemlock (Tsuga). As a specialized member of the Ascomycota division, it targets the living tissues of the bark, disrupting the vascular system and leading to the localized death of twigs and branches.

This disease primarily impacts hemlock trees in both natural stands and landscape plantings. It typically infects trees that are already compromised by environmental stressors, such as drought, frost damage, or physical injury, which allows the fungus to gain entry into the nutrient-rich tissues beneath the bark layer.

The clinical signs of the infection include depressed, discolored lesions on the bark, often accompanied by resin exudation (bleeding). During periods of high humidity, the pathogen produces small, distinctively colored fruiting bodies (perithecia) on the surface of the bark, which are visible to the naked eye and indicate active sporulation.

Environmental conditions play a crucial role in the lifecycle and spread of the fungus. Cool, damp weather during the spring and autumn favors the production and dispersal of spores, which are then carried to healthy hosts by splashing rain or wind currents. Moist conditions are essential for the spores to germinate and successfully colonize new infection sites.

Management of Corinectria tsugae relies heavily on sanitation and cultural practices. Early detection and pruning of infected branches are essential to limit the spread within a tree or a stand. To further reduce the risk, it is recommended to ensure proper tree vigor through balanced fertilization and appropriate site selection, as healthy, non-stressed trees are significantly more resistant to infection.