Irpex

Irpex is a genus of fungi belonging to the family Polyporaceae, most notably represented by Irpex lacteus. These fungi are classified as white-rot agents that actively degrade lignin and cellulose, leading to significant structural damage in both living trees and woody debris within the ecosystem.

The pathogen functions as a necrotrophic parasite and saprotroph. Infection typically begins when fungal spores enter the vascular system or heartwood of a tree through open wounds, frost cracks, or sites damaged by pruning or wood-boring insects. Once established, the mycelium spreads throughout the tree, breaking down the cell walls.

The visual symptoms of Irpex infection include the development of basidiocarps on the bark surface. These fruiting bodies are characterized by a white to cream-colored texture with a distinct tooth-like or poroid hymenophore. Internally, the wood becomes bleached, soft, and fibrous, losing its structural integrity over time.

The proliferation of Irpex is highly dependent on environmental factors, particularly moisture and temperature. Spore production and infection rates peak during periods of high humidity and moderate temperatures. The fungus thrives in shaded, poorly ventilated areas where dead wood is allowed to accumulate, providing a constant reservoir for new infections.

Management and prevention focus primarily on cultural practices. These include maintaining tree vigor to help natural defense mechanisms, prompt removal of decaying or infected limbs, and the use of protective sealants on pruning wounds. Clearing dead woody material from orchards and managed forests is essential to disrupt the pathogen's life cycle.