Bleeding crust fungus

Bleeding crust fungus (Stereum rugosum) is a wood-decaying fungus that acts both as a saprotroph and a weak parasite. In agricultural and forestry settings, it is recognized as a significant agent causing white rot in various species of deciduous trees.

The fungus targets a broad range of hosts, commonly infecting fruit trees such as apples, pears, and plums, as well as forest trees like alder, hazel, and birch. It frequently colonizes trees that are already stressed or wounded, providing an entry point for the fungus to establish itself within the woody tissue.

The most visible symptom is the formation of leathery, resupinate fruit bodies on the bark of trunks and branches. These structures appear wrinkled and can exude a liquid, giving the appearance of "bleeding." Internally, the fungus decomposes the wood, turning it into a white, fibrous, or spongy mass, which severely compromises the tree's structural integrity.

Fungal development is highly dependent on humidity levels and the availability of unprotected entry wounds. Spores are dispersed by wind and rain, settling on pruning cuts, frost cracks, or damaged bark. High moisture levels in the canopy and lack of airflow are critical factors that promote the spread of the pathogen.

The economic impact of Stereum rugosum includes diminished tree vigor, reduced fruit yield, and significant safety hazards due to structural failure and potential breakage of trunks or large limbs. Once established, the fungus is difficult to eradicate, making prevention the primary strategy for orchard health.

• Perform precise pruning and avoid unnecessary injury to the bark.
• Immediately seal all pruning wounds with suitable wound dressings.
• Remove and destroy any wood showing signs of infection to reduce inoculum load.
• Maintain tree health through proper irrigation and nutrient management.