Hypoxylon deustum

Hypoxylon deustum is a serious wood-decaying fungus that acts as a pathogen, primarily responsible for causing white rot in various hardwood species. Formerly classified as Ustulina deusta, this fungus colonizes the wood tissues of trees, leading to significant structural degradation, particularly in the roots and the base of the trunk.

A wide range of host plants, including beech, oak, lime, maple, and various fruit trees, are susceptible to this pathogen. The fungus typically enters the host through wounds, such as branch stubs, pruning cuts, or root damage. Once inside, it colonizes the xylem, feeding on both cellulose and lignin, which fundamentally compromises the tree's internal strength.

The most distinct symptom of infection is the presence of fruiting bodies. In the early stages, they appear as white or greyish flat crusts, but as they mature, they become hard, black, and brittle, resembling burnt charcoal. These structures are often found at the base of the tree or on exposed roots, serving as a clear indicator of a severe underlying rot.

The development of Hypoxylon deustum is favored by high humidity and the poor physiological condition of the host tree. Because the infection is often internal, it may remain hidden for years until the fruiting bodies emerge. During this period, the structural integrity of the tree weakens significantly, posing a high risk of sudden failure or tree fall, which is a major concern for urban arboriculture.

Management of this fungus is primarily preventative because infected wood cannot be restored to its original condition. Key strategies include maintaining high tree vigor to boost natural defenses and carefully performing pruning to avoid creating large wounds. When the fungus is detected, it is often necessary to remove the infected tree and its root system to prevent the spread of spores to healthy neighboring trees.