Chaga mushroom

Pathogen and disease type. The pathogen Inonotus obliquus is a parasitic fungus that causes a white heartwood rot in various hardwood trees. Unlike typical bracket fungi, this pathogen creates sterile conks (the Chaga mushroom) on the bark surface, which are dense, charcoal-like masses of mycelium. The disease gradually causes structural decay within the host tree's trunk.

Susceptible hosts. The fungus primarily infects species of the Betula genus, most notably white birch. However, it can also affect other hardwoods such as alder, beech, elm, maple, and rowan. The infection is most common in mature, dense forests where humidity levels remain high, facilitating the growth of the fungus over many decades.

Symptoms and signs. The characteristic sign of the infection is the presence of hard, black, cracked, and cauliflower-like growths on the trunk. Beneath the bark, the fungus causes severe white rot in the heartwood. Infected trees often exhibit thinning crowns, reduced foliage production, and a general decline in vigor, eventually resulting in trunk breakage due to mechanical instability.

Conditions for development. Infection occurs when spores land on fresh wounds, broken branches, or frost cracks in the tree's bark. The growth of the mycelium is extremely slow, often taking several years for the conk to become visible. Damp conditions and mature tree age are the primary environmental factors that promote the establishment and successful spread of the pathogen.

Impact and control measures. The disease significantly reduces the longevity of the tree and lowers the quality of the timber. To mitigate the spread of Inonotus obliquus, forestry professionals recommend the following strategies:

• Implementing systematic sanitary logging to remove heavily infected trees.
• Preventing mechanical damage to tree trunks during logging and maintenance operations.
• Monitoring forest stands for early signs of fungal conks.
• Promoting overall tree vigor to enhance natural resistance against pathogens.