Stereum

Stereum is a genus of fungi in the family Stereaceae that causes significant wood decay, commonly referred to as white rot. These fungi act as pathogens that colonize woody plants, eventually leading to structural decay through the breakdown of lignin and cellulose within the host's stems and branches.

The fungus primarily targets hardwood species, including a wide range of fruit trees like apples, pears, and plums, as well as various forest trees such as oak and beech. Infection is typically initiated when fungal spores enter the vascular system through open wounds, pruning cuts, bark injuries, or cracks caused by environmental stress.

Symptoms of Stereum infestation include the appearance of tough, leathery fruiting bodies on the bark, which often grow in overlapping clusters. Internally, the wood becomes bleached, soft, and brittle, significantly reducing the mechanical strength of the tree and increasing the risk of trunk failure during wind or heavy storms.

Environmental conditions that favor the development and spread of Stereum include high humidity levels, poor air circulation, and the presence of unprotected exposed wood. The fungal spores are highly mobile, spreading efficiently through wind and splashing water, which makes susceptible wounded trees prime targets for new colonization.

The economic impact of this disease is severe, as it leads to limb dieback and long-term decline of orchard and landscape trees. Effective management involves rigorous sanitation, such as removing infected wood, treating all pruning cuts with appropriate wound sealants, and maintaining tree vigor through proper irrigation and nutrient management to prevent colonization.