Yellow brain fungus

Yellow brain fungus (lat. Tremella mesenterica) is a parasitic and saprotrophic fungus belonging to the Tremellaceae family. While it is primarily a wood-decay agent, in agricultural settings, its presence is a diagnostic marker for decaying organic matter on woody plants that requires management.

This fungus typically colonizes deciduous trees, including various fruit species like apple and pear. It tends to thrive on dead or damaged bark, and its existence is often linked to poor branch maintenance or structural decline of the host plant due to environmental stress or aging.

The most identifiable symptom is the presence of gelatinous, bright orange or yellow fruiting bodies. These structures exhibit a brain-like, convoluted appearance. During dry periods, they shrivel into a nearly invisible crust, but rapidly rehydrate into a gelatinous mass following rainfall.

Fungal development is highly dependent on humidity and moisture content of the woody tissue. Spores are dispersed by wind and rain, infecting susceptible areas of the tree, such as pruning wounds, bark cracks, or necrotic zones created by other pests or physical injuries.

Effective management focuses on mechanical removal and environmental control. Gardeners should prune out infected branches, remove dead wood from the orchard, and ensure proper sanitation practices. Applying copper-based fungicides to pruning sites helps protect the wood from further colonization and secondary infections.