Bjerkandera adusta

Bjerkandera adusta, commonly known as the smoky bracket, is a wood-decay fungus of the order Polyporales. It acts as a primary pathogen causing white rot in a wide variety of hardwood tree species. The fungus is particularly noted for its ability to degrade both lignin and cellulose, leading to a rapid loss of structural integrity in the timber of infected hosts.

The host range for this pathogen includes numerous deciduous trees, such as beech, birch, oak, poplar, and several fruit-bearing species. It frequently infects trees that are already stressed by environmental factors, drought, or physical injury. The presence of wounds on the bark, frost cracks, or improper pruning cuts provides a direct pathway for the fungus to infiltrate the heartwood or sapwood.

Identification of the disease is based on the appearance of its characteristic fruiting bodies. These bracket-shaped mushrooms are typically greyish-brown on the upper surface with a distinct dark, almost charred-looking margin, which gives the fungus its common name. Internally, the infected wood becomes bleached, soft, and fibrous, losing its structural strength and making the tree prone to windthrow.

Environmental conditions that favor the spread of Bjerkandera adusta include high moisture levels and poor aeration within dense forest stands or orchards. The fungus spreads primarily through airborne spores produced by the fruiting bodies. These spores can survive in harsh conditions and germinate rapidly when they land on susceptible, moist wood surfaces exposed by damage.

Managing this fungus requires a combination of cultural practices and diligent orchard management to prevent wood decay:

• Prune dead or diseased branches correctly to promote rapid callus formation.
• Apply wound sealants or fungicides to significant bark injuries immediately after occurrence.
• Remove and destroy heavily infested wood to reduce the local spore load.
• Maintain tree vigor through balanced nutrition and proper watering schedules to boost natural defenses.