White trunk rot

White trunk rot is a destructive plant disease caused by the fungus Phellinus igniarius, a type of wood-decay fungus belonging to the Polyporaceae family. This pathogen is notorious for its ability to cause extensive internal decay, progressively transforming the heartwood into a soft, fibrous, and white mass.

The host range of this fungus includes various deciduous trees. It is frequently observed on species such as black walnut, birch, aspen, alder, and willow. The infection typically establishes itself through entry points such as broken branches, pruning wounds, or frost cracks, allowing the mycelium to colonize the interior of the trunk.

The most reliable sign of the disease is the presence of perennial conks (fruiting bodies) on the surface of the tree. These structures are typically hoof-shaped, woody in texture, and dark-colored, often showing distinct concentric zones. Internally, the wood becomes bleached and brittle, often separated by thin, dark fungal lines that define the advancement of the decay.

Environmental factors favoring the development of the fungus include prolonged high humidity and the presence of exposed woody tissues. Phellinus igniarius reproduces by releasing spores from the undersides of the fruiting bodies, which are then disseminated by wind or rain to susceptible wounds on healthy trees, initiating new infection cycles.

The harmful effects of white trunk rot are significant, leading to structural weakness and structural failure of the host. Management strategies focus on sanitation and preventative care. Key actions include pruning damaged limbs correctly to promote rapid callus formation, painting large wounds with protective sealants, and removing severely infected trees or individual conks to reduce the local spore load.