Yellow-felted parchment fungus

The yellow-felted parchment fungus (Stereum subtomentosum) is a wood-decaying fungus that primarily acts as a pathogen of hardwood trees. It belongs to the Russulales order and is widely known for inducing white rot, a process in which the fungus enzymes break down lignin and cellulose within the host's woody tissue.

It typically targets a broad spectrum of deciduous species, frequently impacting orchard trees such as apples, pears, and plums, as well as various forest trees like birches and alders. The fungus generally gains access to the tree through open wounds caused by pruning, storms, frost cracks, or mechanical damage to the bark.

Visible signs of an infestation include the growth of leathery, bracket-like fruiting bodies on the trunk or branches. These bodies are characterized by a yellowish-brown, felt-like surface. Internally, the wood undergoes significant changes, becoming soft and discolored with distinct dark zone lines that delineate the areas actively being degraded by the mycelium.

Development and spread are heavily influenced by environmental factors such as high ambient humidity and moderate temperatures. The spores are primarily air-borne, traveling on breezes or splashing during rain to settle on susceptible exposed wood surfaces. Once established, the mycelium spreads systemically within the tree, often remaining hidden until structural failure occurs.

The impact of this fungus is severe, as it compromises the structural integrity of the tree, leading to branch breakage and eventual host mortality. Control strategies focus on strict hygiene:

• sanitizing pruning tools regularly;
• painting large wounds with specialized sealants;
• removing deadwood promptly to eliminate spore sources;
• maintaining overall tree vigor through proper fertilization and watering.