Xylohypha ortmansiae

The fungus Xylohypha ortmansiae is a recognized pathogen known for causing localized necrotic lesions in woody plants. This fungus acts as a facultative parasite, often exploiting compromised areas of bark or cambium to establish its colony. By penetrating deeper into the vascular tissues, it disrupts nutrient transport, leading to the gradual decline of the affected branch or stem section.

The host range of this pathogen includes various ornamental and forest trees. It is particularly aggressive toward trees that have suffered from environmental stressors, such as drought, frost cracks, or mechanical damage from wind and pruning. Younger specimens and trees in dense plantations are significantly more susceptible to successful colonization by the fungal spores.

Symptoms of the infection typically begin as localized discoloration of the bark, which soon develops into sunken necrotic ulcers. These lesions are often accompanied by longitudinal cracking of the bark and the potential weeping of sap. In later stages, the affected tissue turns brittle and dark, eventually flaking off to reveal the underlying wood infected by the mycelium.

Development and dissemination are highly dependent on high humidity and moderate temperatures, which favor spore production and germination. The spores are primarily dispersed by wind and rain splashing, making the infection cycle highly efficient during wet seasons. Poor orchard or forest sanitation, particularly the presence of dead wood and leaf litter, provides a reservoir for the pathogen to survive during winter months.

Effective management and protection strategies are grounded in rigorous sanitation protocols. It is essential to prune out and destroy all infected branches immediately upon detection, ensuring that all tools are sterilized with alcohol or bleach between cuts to prevent mechanical transmission. Chemical control using preventive fungicides can be an effective measure when applied consistently during the growing season to protect healthy tissue from initial infection.