Alder Cytospora canker

Alder Cytospora canker, caused by the fungus Cytospora fugax, is a significant bark-infecting disease that affects various alder species. This pathogen is classified as a necrotrophic parasite, meaning it actively kills host tissue, leading to the development of necrotic lesions on branches and the main trunk of the tree.

The primary hosts of this pathogen are trees of the genus Alnus. The disease is particularly aggressive in trees that are under environmental stress, such as those suffering from soil water deficit or waterlogging, as well as those that have sustained bark damage from frost, pruning tools, or wood-boring insects.

Symptoms initially appear as localized discolorations or sunken areas on the bark. As the infection progresses, the bark dies, cracks, and may peel away, revealing the underlying woody tissue. During wet periods, reproductive structures known as pycnidia develop within the dead bark, releasing masses of spores that emerge as tiny, jelly-like, yellowish to orange tendrils.

The development of Cytospora fugax is highly dependent on humidity and moisture. Spores are easily disseminated by wind, splashing rain, and through the activity of bark beetles and other insects that carry the spores from infected trees to fresh, susceptible wounds on healthy individuals.

The economic and ecological impact of this canker includes reduced growth, limb loss, and in severe cases, the death of the tree. Effective disease management strategies include the removal and destruction of infected wood, proper pruning techniques to avoid leaving large stubs, and maintaining overall tree vigor through appropriate site selection and adequate moisture management to ensure resistance.