Birch polypore

Pathogen and type of disease: The Birch polypore (Piptoporus betulinus) is a wood-decaying fungus that causes a lethal condition known as brown rot. Classified within the Fomitopsidaceae family, it is a specialized parasite that exclusively targets birch trees, leading to the internal decomposition of the woody tissue.

Affected plants: The fungus primarily attacks various species of birch, such as Betula pendula and Betula pubescens. It tends to colonize trees that are already stressed, aged, or those with significant mechanical wounds on their bark, which serve as entry points for the fungal mycelium.

Symptoms and signs: The presence of the pathogen is indicated by the growth of annual, hoof-shaped, or kidney-shaped fruiting bodies protruding from the trunk. The surface of these fruiting bodies is typically smooth and light brown. Internally, the wood loses its tensile strength, becomes brittle, turns a dark brown color, and fractures into distinct cubes as the cellulose is consumed.

Conditions for development: Spores of the fungus are dispersed by wind and require moisture to germinate after settling on damaged bark. Once the mycelium enters the tree, it spreads throughout the heartwood. The development is often slow, and the tree may appear healthy for several years before the internal decay becomes critical and the fruiting bodies emerge.

Damage and preventive measures: The fungus causes severe wood rot, rendering the tree unstable and prone to collapse. Management strategies focus on forest hygiene, which includes:

• systematic removal of infected and fallen trees;
• avoiding bark damage during silvicultural activities;
• maintaining high biodiversity to promote natural resistance;
• monitoring forest stands for the emergence of visible sporocarps.