Willow crust fungus

The willow crust fungus (Cytidia salicina) is a species of fungi in the family Corticiaceae. It typically acts as a saprotroph or a weak parasite, colonizing the bark of willow trees and contributing to the degradation of woody tissues in specific environmental conditions.

The primary hosts for this pathogen are species of the genus Salix. The fungus preferentially targets branches and trunks, especially those that are already stressed due to age, environmental pressure, or pre-existing mechanical damage that exposes the inner bark layers to fungal spores.

The most visible signs of infection are the fungal fruit bodies, which appear as orange to reddish, disc-shaped patches on the surface of the bark. These structures are leathery or rubbery when fresh and often become darker, reddish-brown, and brittle during drier periods.

Environmental factors are critical for the lifecycle of Cytidia salicina. The pathogen thrives in humid, shaded environments. High moisture levels on the bark surface facilitate the germination of basidiospores, allowing the fungus to spread efficiently across the host's surface.

Management of this fungus focuses on preventative silvicultural practices. Key strategies include the regular removal of dead or dying branches, maintenance of tree vigor through appropriate fertilization and water management, and ensuring sufficient airflow within the canopy to minimize persistent humidity on the bark.