Rigidoporus ulmarius

Rigidoporus ulmarius is a wood-decaying fungus that primarily acts as a pathogen causing white rot in various deciduous trees. It is a perennial fungus known for its capability to degrade both lignin and cellulose within the wood, leading to significant structural damage to the host plant's trunk and root collar.

While the fungus is frequently associated with elm trees (Ulmus species), its host range is quite broad. It can infect various species of poplar, willow, plane trees, and even certain fruit tree varieties. The fungus colonizes the tree through wounds or root contacts, eventually establishing a persistent infection that can remain hidden inside the heartwood for many years.

The most distinctive visual symptom is the formation of large, woody, bracket-shaped fungal conks, typically appearing near the base of the tree or on major roots. Internally, the wood becomes bleached, spongy, and brittle as the fungus consumes the structural components of the timber. This degradation significantly reduces the tree's stability and increases the risk of structural failure.

The development of the disease is favored by high humidity and temperate climates, which promote spore dispersal and mycelial growth. The pathogen spreads via airborne basidiospores that settle on fresh wounds, pruning cuts, or fissures in the bark. Once established, the mycelium spreads slowly but steadily, often causing internal decay that remains undetected until the late stages of infection.

Effective management strategies rely heavily on preventive silvicultural practices. It is crucial to minimize tree wounding, maintain tree vigor through proper fertilization and watering, and promptly treat any mechanical injuries with protective sealants. If an infection is confirmed, removal of the infected tree, including the stump and major root systems, is usually necessary to stop the spread of the fungus to neighboring trees.