Septobasidiaceae

The Septobasidiaceae family represents a unique group of basidiomycete fungi known for their symbiotic relationship with scale insects. Unlike typical plant pathogens that invade the host tissue directly, these fungi form protective mats over colonies of insects living on the bark of trees and shrubs, creating a complex microenvironment that can be detrimental to the plant.

These fungi predominantly affect woody plants, including various fruit trees like apples, pears, and citrus. The presence of the fungus is often a strong indicator of a scale insect infestation, as the fungus relies on the metabolic byproducts of these insects to sustain its growth, while physically covering the host plant's bark.

Symptoms appear as thick, leathery, or velvety patches on the surface of branches and trunks. These mats are often tan, brown, or blackish and can eventually spread over significant portions of the woody structure. While they do not cause decay in the timber, they interfere with the natural gas exchange of the plant by blocking the lenticels on the bark.

The development and spread of Septobasidiaceae are favored by humid conditions and the presence of healthy scale insect colonies. Because the fungus thrives under the cover provided by the mats, it is protected from many environmental stressors. If left untreated, the covering can persist for years, gradually expanding as the scale insect population flourishes.

Effective management focuses primarily on the control of the scale insects, as they are the foundational host for the fungus. Chemical control using horticultural oils or systemic insecticides applied during the crawler stage of the insects is highly recommended. Pruning infested branches and cleaning the bark during the dormant season are essential cultural practices to reduce the fungal footprint and improve overall tree vigor.