Ustulina rot

The causative agent of this disease is the fungus Ustulina deusta (syn. Hypoxylon deustum), a member of the Ascomycota phylum. It is a potent pathogen responsible for white rot, a form of wood decay that breaks down the structural components of the tree's trunk and root system.

This fungus typically affects a wide range of broad-leaved trees, including common orchard species such as apple and plum, as well as forest trees like beech, oak, and maple. The pathogen generally gains entry through bark wounds, pruning cuts, or frost cracks, where it slowly colonizes the heartwood and sapwood.

Symptoms are identified by the presence of carbonaceous, coal-black, brittle stromata that appear on the bark surface, particularly near the base of the tree. Internally, the wood exhibits a bleached, white-rot appearance interspersed with distinctive black zone lines. These lines represent areas where the fungus has compartmentalized its growth within the decaying wood.

Disease progression is heavily influenced by high moisture levels and poor tree vigor. The fungus spreads primarily through spores dispersed by wind or splashing water during rainy periods. Once spores land on a fresh wound, they germinate and initiate the colonization process, which can take several years to become clinically visible.

The economic and ecological impact of Ustulina rot is significant, as it leads to brittle wood, branch breakage, and potential tree failure. Management strategies focus on preventive care, including sanitary pruning to remove infected material, protecting fresh cuts with fungicides, and ensuring trees remain healthy and resilient through proper irrigation and soil management.