Orange crust fungus

Orange crust fungus (scientifically known as Peniophora aurantiaca) is a member of the Peniophoraceae family. This fungus acts as a wood-decaying organism that primarily targets the bark of deciduous trees. While it often functions as a saprotroph, it frequently behaves as a weak parasite, exploiting trees that are already suffering from stress or mechanical damage.

The host range of Peniophora aurantiaca is notably concentrated on alder species (Alnus). The fungus invades the host through bark fissures, pruning wounds, or areas weakened by abiotic factors like frost or drought. Once established, the mycelium spreads through the bark tissue, causing structural and physiological damage to the tree's outer defense layers.

The primary symptom is the emergence of distinctive, thin, orange to reddish-orange crust-like fruit bodies on the surface of branches and trunks. As the infection progresses, the infected bark becomes brittle, starts to crack, and eventually peels off. This process restricts nutrient flow and can lead to branch dieback, especially in weakened or elderly trees in damp environments.

Environmental conditions play a critical role in the development of this fungus. High relative humidity, persistent rainfall, and poor airflow in dense thickets provide the perfect conditions for spore germination and colonization. The spores are typically wind-dispersed, allowing the fungus to spread rapidly across woodlands or damp garden areas during wet seasons.

Management strategies focus on reducing the pathogen load and improving tree vigor:

• Prune and remove all infected branches to reduce spore sources.
• Treat large pruning wounds with protective fungicides or wound sealants.
• Improve air circulation through selective thinning of forest or garden plots.
• Maintain tree health through proper fertilization and watering to improve natural defenses.