Athelia arachnoidea

Athelia arachnoidea is a species of corticioid fungus that functions primarily as a pathogen capable of affecting various plant species. Although historically considered a harmless saprotroph that decomposes dead wood or lichen, it has been identified as a significant parasitic agent that can aggressively colonize the bark, foliage, and stems of live plants under specific environmental conditions.

The host range of this fungus is quite broad, often targeting ornamental trees and shrubs in nurseries or landscape plantations. It is particularly noted for its ability to overgrow mosses and lichens found on tree trunks, eventually transitioning to the living bark. In greenhouses or densely planted gardens, it can cause severe stress to perennials, leading to a decline in aesthetic and physiological quality.

The most visible symptom of an infestation is the presence of a white, web-like mycelium that spreads across the surface of the plant organs. This growth can appear as a thin veil, masking the underlying tissue. As the pathogen develops, it forms dense mats that deprive the host of sunlight and oxygen. Sustained infestation often results in necrotic spots, localized tissue death, and the eventual decay of smaller, weaker twigs and shoots.

The development of Athelia arachnoidea is highly dependent on humidity. It flourishes in stagnant air and environments with high moisture levels, which often occur in overcrowded plantings or areas with poor drainage. The pathogen spreads via spores disseminated by splashing water, wind, or physical contact with contaminated tools and human hands during maintenance operations.

Effective management and prevention of this fungal infection rely on environmental manipulation and chemical control:

• Pruning plants to improve airflow and reduce humidity levels within the canopy.
• Maintaining proper plant spacing to prevent the microclimate from becoming overly humid.
• Removing and disposing of heavily infested plant materials to lower the inoculum level.
• Application of approved fungicidal treatments during early stages of infection.