Hen of the woods

Hen of the woods (Grifola frondosa) is a parasitic wood-decay fungus that causes white root rot and butt rot in woody plants. While it is widely recognized as an edible species, in forestry and ornamental arboriculture, it is considered a significant pathogen that can cause severe damage to the structural integrity of mature trees.

The disease is caused by a basidiomycete fungus that acts as a necrotrophic parasite. It enters the tree through wounds or root damage, gradually decomposing the structural components of the wood, specifically cellulose and lignin. This process leads to a decay that significantly weakens the base of the tree.

This pathogen primarily targets deciduous tree species, including oak, maple, beech, and chestnut. The infection typically establishes itself in the roots and the base of the trunk. Because the mycelium grows internally, the symptoms are often hidden for several years, making early detection a significant challenge for foresters.

Typical signs of infestation include the presence of large, frond-like fruiting bodies appearing at the base of the tree during late summer and autumn. The infected wood becomes soft and brittle, leading to a high risk of windthrow. Often, the crown of the affected tree shows signs of decline, such as premature yellowing and thinning leaves.

• development of large, clustered fruiting bodies at the tree base;
• soft, light-colored rot within the roots and lower trunk;
• decreased structural stability and increased risk of windthrow;
• premature leaf drop and crown thinning;
• mycelial expansion throughout the root zone.

Development is favored by high soil moisture levels, soil compaction, and existing mechanical damage to the trunk or roots. The fungus spreads via spores carried by wind and through root-to-root contact in dense forest stands. The pathogen can persist in the soil and woody debris for a long period, posing a threat to neighboring trees.

Management practices focus on preventative measures and promoting tree vigor. Key strategies include avoiding mechanical trauma to the root zone, ensuring proper soil drainage, and performing regular sanitation to remove heavily infested trees and their root systems. As there are no curative chemical treatments for internal trunk rot, monitoring and sanitation remain the primary defense.