Oak crust

Oak crust (lat. Peniophora quercina) is a common wood-decay fungus within the family Peniophoraceae. It is primarily known for causing white rot in a variety of deciduous trees. While it is frequently observed as a saprotroph breaking down dead wood, it can act as a secondary parasite on stressed or damaged hosts.

The fungus predominantly targets broad-leaved species, with oaks (Quercus spp.), beech, and hazel being the most common hosts. It infiltrates the host through wounds, broken branches, or exposed heartwood, where it utilizes specialized enzymes to break down lignin, effectively weakening the structural integrity of the woody tissue.

Infection symptoms are characterized by the appearance of perennial fruit bodies. These fruit bodies are thin, crust-like, and firmly attached to the bark surface, appearing in shades of gray, ochre, or lilac-brown. Beneath the crust, the wood often becomes bleached and brittle, a diagnostic sign of the white rot process typical of Peniophora species.

Environmental conditions play a critical role in the dispersal and colonization success of the fungus. High humidity and cool-to-moderate temperatures provide the optimal environment for spore germination and mycelial expansion. Dead wood left on the forest floor or in tree canopies acts as an important reservoir, facilitating the spread of spores to healthy or vulnerable trees.

Management and prevention focus on enhancing tree vigor and minimizing pathways for fungal entry. Key practices include:

• Implementing regular sanitation pruning to remove dead or infected branches.
• Proper disposal of colonized woody debris to reduce inoculum sources.
• Protecting the bark from mechanical injury during maintenance activities.
• Monitoring trees for signs of decay, especially after storm damage or severe drought.