Bleeding sap rot

Bleeding sap rot is caused by the wood-decaying fungus Stereum sanguinolentum, a basidiomycete responsible for significant timber degradation. It acts as both a saprotroph and a wound pathogen. The name refers to the distinctive blood-like droplets that ooze from the fresh, leathery fruit bodies when they are damaged or scraped.

The disease primarily targets coniferous trees, being particularly destructive to spruce, fir, and Douglas Fir. The fungus utilizes wounds as primary entry points, which can be caused by wind-throw, branch breakage, insect activity, or mechanical damage occurring during logging operations and forest thinning procedures.

Symptoms of the infection include the presence of thin, crust-like fruiting bodies that appear grayish-brown on the bark or exposed wood. Internally, the wood undergoes a transformation characterized by a reddish-brown discoloration, eventually developing into a mottled, brittle decay as the fungus breaks down the structural integrity of the timber.

The spread of the disease is highly dependent on environmental conditions, with high humidity and moderate temperatures favoring spore germination. Spores are wind-dispersed and land on exposed wood surfaces, where they germinate and initiate mycelial growth, which spreads systemically through the heartwood of the tree.

Economic impact is significant due to the loss of high-quality wood and the increased risk of stem breakage. Management strategies focus on forest hygiene, including the removal of infected debris and individual trees. Silvicultural practices aimed at reducing stem damage are essential to prevent the entry of this fungus into healthy stands.