Xylaria friesii

Xylaria friesii is a pathogenic fungus belonging to the class Sordariomycetes, known for causing white rot in various hardwood species. Unlike many other fungi that attack only dead wood, this species can act as a secondary parasite, colonizing stressed or wounded living trees. Its ability to decompose lignin and cellulose makes it a significant factor in timber decay and structural degradation of garden trees.

The host range of Xylaria friesii primarily includes broad-leaved trees. It typically gains entry to the host through mechanical wounds, pruning cuts, or frost cracks on the bark. Once inside, the mycelium spreads throughout the sapwood and heartwood, utilizing the nutrients within the host tissues and gradually breaking down the cellular structure of the tree.

Visual symptoms include the emergence of characteristic black, club-shaped or finger-like stromata on the surface of the bark. These are the reproductive structures that release spores. Internally, the wood becomes discolored, turning light in color, and loses its structural integrity, eventually becoming soft, spongy, and brittle, which significantly increases the risk of tree failure during storms.

The development of the fungus is highly dependent on humidity and moisture levels. High ambient humidity and moderate temperatures facilitate the rapid spread of spores through the air. The fungus is persistent; it can survive in decaying wood remnants, leaf litter, and even in the soil, making it a difficult pathogen to eradicate if sanitation practices are neglected in the orchard.

Effective management and protection strategies include a range of cultural practices aimed at minimizing exposure:

• Prompt removal of diseased wood or entire infected trees to eliminate inoculum sources.
• Protection of pruning wounds with fungicidal pastes or wound dressings.
• Maintenance of tree vigor through proper irrigation and balanced fertilization.
• Sterilization of pruning tools between trees to prevent the mechanical transmission of spores.