Exidia

Exidia is a genus of basidiomycete fungi belonging to the Auriculariaceae family. In the field of arboriculture and agronomy, these fungi are often categorized as saprotrophs or facultative parasites that colonize weakened or decaying parts of woody plants. While they are not primary pathogens of agricultural crops, their presence indicates compromised bark integrity and excessive moisture levels.

The causal agents are various species within the Exidia genus, known for their jelly-like fruiting bodies. They operate primarily as wood-decay fungi (xylotrophs), breaking down organic matter. By colonizing the bark, they may accelerate the degradation process, which can negatively affect the overall vitality of the host tree if the plant's defenses are already weakened by environmental stress.

The fungus affects a variety of broadleaf trees, including species like oak, birch, and various fruit trees. The main symptoms are characteristic gelatinous, folded, or tuberculate fruiting bodies appearing on the branches or trunks. These structures may appear translucent, white, or dark-colored, and become smooth and shiny when saturated with rainwater.

Development and spread are favored by high humidity, poor air circulation, and stagnant water on the surface of the bark. Spores are disseminated by wind and splashing rain. The fungi prefer colonization sites where the bark is already dead, damaged by frost, or compromised by mechanical injuries, providing a substrate for the mycelium to establish.

The harmful impact lies in the potential for bark degradation and the creation of entry points for more aggressive wood-rot pathogens. Prevention and control strategies include regular sanitary pruning to remove infected branches, improving tree canopy aeration, and ensuring wounds are properly sealed with pruning sealers. Maintaining overall tree health through proper fertilization and watering is the best defense against fungal colonization.