Stereum hirsutum

Stereum hirsutum, commonly known as the hairy curtain crust, is a basidiomycete fungus that functions primarily as a wood-decay saprotroph. While it plays a key role in the nutrient cycle of forests by decomposing dead wood, it can act as a pathogen in orchards and managed landscapes, leading to significant structural damage in living trees.

This fungus targets a wide range of broad-leaved host plants. Commonly affected species include apple, pear, plum, oak, beech, and birch trees. The fungus is particularly aggressive when it finds entry points into the heartwood or sapwood of trees that are already suffering from stress, mechanical injuries, or poor pruning practices.

The primary symptom of infection is the development of rigid, leathery, shelf-like fruiting bodies with a distinctive hairy, yellowish-orange upper surface on the bark. Inside the tree, the mycelium causes white rot, which degrades lignin and cellulose. This process compromises the mechanical integrity of the trunk or branches, often leading to premature breakage and windthrow.

The development and spread of Stereum hirsutum are heavily dependent on environmental conditions, specifically moisture and temperature. Spores are dispersed through the air and water, infiltrating vulnerable sites such as pruning cuts, frost cracks, or sunscald wounds. Once the fungus establishes itself, it creates a persistent source of inoculum that can infect surrounding trees if left unmanaged.

Effective management and prevention focus on maintaining tree vigor and protecting exposed tissues. Key strategies include:

• Promptly sealing large pruning wounds with appropriate dressings.
• Sanitizing pruning tools between trees to prevent cross-contamination.
• Removing and destroying infected wood or dead branches from the orchard.
• Maintaining optimal soil health and hydration to support the tree's natural defense mechanisms.