Silver leaf fungus

Silver leaf fungus (Chondrostereum purpureum) is a basidiomycete fungus that acts as a serious plant pathogen. It is a wound parasite that can persist in the environment as a saprotroph on decaying wood before infecting healthy host plants. This fungus is globally recognized as the primary cause of the systemic disease known as silver leaf.

The disease primarily affects woody species, particularly those in the Rosaceae family such as apples, plums, cherries, and pears. The diagnostic symptom is a metallic, silvery, or pearlescent sheen on the foliage. This coloration occurs due to the breakdown of leaf tissues and the accumulation of air pockets beneath the epidermis, which disrupts normal light reflection and leaf physiology.

The life cycle involves the release of basidiospores from bracket-like fruiting bodies that typically appear on dead wood. These spores enter the tree through mechanical wounds, pruning cuts, or winter damage. Once inside, the fungus invades the xylem tissue, releasing phytotoxins that are transported upward, causing the characteristic silvering of the canopy leaves far from the site of the initial infection.

Optimal conditions for infection include damp, cool weather, which promotes spore release and germination on unprotected pruning wounds. If left unchecked, the fungus systematically colonizes the wood, causing a progressive decline in tree health, browning of the internal wood, and eventually death of individual branches or the entire tree.

Management of this pathogen is challenging because the mycelium remains deep within the wood. Control strategies must be preventative rather than curative:

• Prune trees during dry weather periods when spore activity is lower.
• Sterilize all pruning tools with a disinfectant before moving between trees.
• Seal all pruning cuts immediately using specialized wound paints or fungicides.
• Regularly inspect the orchard for fruit bodies on deadwood and remove them.
• Remove and destroy severely infected trees to prevent the spread of spores to healthy neighbors.