Hapalopilus rutilans

Hapalopilus rutilans is a wood-decay fungus responsible for causing white rot in a variety of deciduous tree species. As a facultative pathogen, it primarily colonizes weakened, stressed, or aging trees, breaking down lignin and cellulose within the heartwood and sapwood, which significantly compromises the structural integrity of the host plant over time.

This fungus exhibits a wide host range, frequently infecting hardwoods such as oak, beech, birch, and various fruit-bearing trees. When a tree is already compromised by environmental stressors—such as drought, soil compaction, or physical wounds from improper pruning—Hapalopilus rutilans can exploit these vulnerabilities to establish its mycelial network deep within the woody tissue.

The primary clinical signs of infestation include the appearance of annual or perennial fruiting bodies, typically characterized by their reddish-brown to cinnamon-colored upper surfaces. Internally, the infected wood turns pale, soft, and fibrous. A notable chemical identifier is the reaction of the decayed wood to alkaline solutions, which turns the tissue a distinct, vivid violet color, confirming the presence of the pathogen.

The development of this disease is highly dependent on humidity and ambient temperature. Moisture facilitates spore germination, while tree wounds serve as infection courts. Poor aeration and lack of pruning hygiene contribute significantly to the rapid spread of the fungus throughout an orchard or a forest stand, as the spores travel through the air to land on unprotected wounds.

Managing and preventing the spread of Hapalopilus rutilans requires a proactive approach centered on tree vitality:

• Remove and destroy all infected woody debris to lower inoculum levels;
• Apply antifungal protective paints or pastes to large pruning wounds to block entry;
• Monitor trees for early signs of decay and fruiting body formation;
• Maintain optimal tree health through proper fertilization and irrigation to strengthen natural defenses.