Irpex lacteus

Irpex lacteus is a species of crust fungus in the family Polyporaceae that acts as a wood-decay pathogen. It is a facultative parasite, meaning it thrives primarily as a saprotroph on dead wood but can aggressively colonize weakened, injured, or aging living trees, causing extensive white rot in the structural tissues.

The fungus affects a wide range of broad-leaved trees, including significant damage to common orchard species such as apple, pear, plum, and cherry trees. Orchards with older trees or those suffering from environmental stress, such as frost cracks or sunscald, are at a significantly higher risk of being infected by this pathogen.

The clinical symptoms include the appearance of annual or perennial basidiocarps, which typically form a toothed, white-to-cream-colored hymenophore on the bark surface. Internally, the wood undergoes degradation of lignin and cellulose, turning into a brittle, fibrous, and pale mass. Eventually, the tree loses structural integrity, leading to branch breakage and total tree decline.

Environmental conditions conducive to the development and spread of Irpex lacteus include high humidity and temperatures ranging from 15 °C to 25 °C. Spores are dispersed through wind and splashing water, settling on tree wounds, pruning cuts, or dead patches of bark, where the mycelium begins its invasive growth into the woody interior.

The economic impact of this fungus is significant as it shortens the lifespan of fruit trees and reduces crop yields by impairing nutrient transport. Key management and preventive strategies include:

• Performing regular sanitary pruning to remove infected wood, followed by immediate application of wound sealants.
• Protecting tree trunks from sunscald and frost damage using protective white coatings.
• Improving overall tree vitality through proper fertilization and pest management.
• Ensuring complete removal of decaying stumps and infected woody debris to eliminate the primary sources of inoculum in the orchard.