Ustilina deusta

Ustilina deusta (syn. Hypoxylon deustum) is a significant wood-decaying fungus belonging to the division Ascomycota. It acts as a facultative parasite, primarily causing white rot in a wide range of broad-leaved trees, including beech, oak, lime, and various fruit trees. The fungus is known for its ability to degrade both cellulose and lignin, leading to structural instability in host trees.

The disease typically affects the roots and the basal part of the trunk. Infected trees often show no outward signs of distress until the fungal fruiting bodies appear. These structures appear as crusty, coal-black, plate-like growths at the base of the stem or on the root collar, giving the tree an appearance of being scorched by fire.

Regarding its biology, the fungus enters the host through wounds, pruning cuts, or damaged roots. Once established, the mycelium colonizes the sapwood and heartwood. The life cycle involves the production of both asexual conidia and sexual ascospores, which are dispersed by wind or rain, facilitating the colonization of neighboring trees in damp, crowded, or poorly managed environments.

Environmental conditions that favor the spread of Ustilina deusta include high humidity and persistent moisture around the root zone. The fungus thrives in stands that are stressed by drought, soil compaction, or physical damage. Once the internal wood tissue is sufficiently degraded, the risk of tree failure increases significantly, especially during storms or high wind events.

Control measures for this pathogen center on prevention and proper forest management. Key strategies include avoiding mechanical damage to tree trunks during maintenance, ensuring proper tree health through balanced fertilization, and rapid removal and destruction of infected trees. Because the fungus can persist as a saprophyte, stumps of infected trees should also be removed to eliminate potential sources of inoculum.