Septobasidium aleuritis

Septobasidium aleuritis is a fungal pathogen belonging to the Basidiomycota phylum, known for causing specific bark diseases on woody plants. It is highly recognized for its symbiotic relationship with scale insects (Coccoidea). The fungus covers colonies of these insects with its mycelial mats, creating distinctive protective structures that look like crusts or felt-like patches on the surface of branches.

The primary host for this fungus is the tung tree (Aleurites fordii). The disease is primarily found in regions where these trees are cultivated under high humidity and warm temperatures. Because the fungus thrives in specific microclimates created on the bark, it is essentially a disease that targets areas already suffering from underlying pest pressure.

Symptoms are manifested by the appearance of thickened, leathery, or velvety mats on the bark of trunks and branches. These mats vary in color from light brown to greyish-tan. As the fungal colony expands, it can physically constrict the bark, leading to minor cracks, necrosis of the outer tissues, and a general decline in the vitality of the affected branch or twig.

Environmental conditions such as prolonged rainfall, fog, and inadequate air circulation within the tree canopy are the main drivers of disease propagation. Since the fungus relies on the presence of scale insects for colonization, the disease development cycle is synchronized with the insect population growth. High moisture facilitates spore germination and mycelial spread across the host plant.

Management and prevention of Septobasidium aleuritis require an integrated pest and disease management (IPDM) approach to address both the fungal growth and the associated insect population.

• Rigorous control of scale insect populations using systemic or contact insecticides during the crawlers' activity period.
• Pruning and removal of severely infected branches to reduce the inoculum pressure in the orchard.
• Application of copper-based fungicides during the dormant season to sanitize the bark surface.
• Improving site conditions by ensuring proper pruning to allow sunlight and airflow into the canopy.