Brown trunk rot

Brown trunk rot, caused by the fungus Fomitopsis officinalis (commonly known as the quinine conk), is a severe wood decay disease that primarily affects long-lived conifer species. As a brown rot pathogen, it specializes in breaking down cellulose within the heartwood, which causes the wood to crack into cubic pieces and eventually crumble into a fine powder.

This fungus is notably found in several conifer species, with the Douglas Fir (Pseudotsuga menziesii) being a primary host in forest ecosystems. The infection usually initiates through branch stubs or deep wounds in the bark, where spores can germinate and mycelium can colonize the exposed wood tissue.

The most visible sign of infection is the presence of large, perennial conks that grow on the stems of affected trees. These fruiting bodies are typically hoof-shaped or cylindrical, white to yellowish in color, and have a distinctively bitter taste. Their presence on a tree usually indicates that extensive internal heart rot has already occurred.

Environmental factors such as high humidity and the presence of old-growth timber favor the development of Fomitopsis officinalis. The fungus spreads through airborne spores released from the fruiting bodies, which then settle on wounded or susceptible wood surfaces of adjacent trees, perpetuating the infection cycle over many years.

Management of brown trunk rot focuses primarily on silvicultural practices designed to promote stand health. Key measures include timely removal of infected trees during sanitation thinning, minimizing physical damage to standing timber during logging operations, and maintaining diverse age structures to prevent widespread outbreaks in susceptible coniferous stands.