Chondrostereum

The fungus Chondrostereum purpureum is the primary pathogen responsible for what is commonly known as "Silver Leaf disease." As a basidiomycete, it acts as a wood-decay fungus that colonizes the xylem of the host plant, systematically destroying internal structures and producing toxins that spread throughout the tree.

A wide range of woody species is susceptible, particularly members of the Rosaceae family such as apples, pears, plums, and cherries. Additionally, various deciduous forest trees, including poplars, willows, and maples, can serve as hosts, often acting as reservoirs for the pathogen within the local ecosystem.

The hallmark symptom is a distinct metallic, silvery appearance of the leaves. This is caused by the separation of the leaf epidermis from the mesophyll due to the fungal toxins, creating air spaces that reflect light. Later, leathery, bracket-shaped fruiting bodies with a characteristic purple-tinted underside appear on dead or dying branches.

The disease cycle depends heavily on moisture; fungal spores are released during wet weather and enter the tree through wounds or pruning cuts. Once established, the fungus grows internally, making it difficult to treat with systemic fungicides, which emphasizes the critical importance of preventing infection.

The impact of this disease is severe, leading to limb dieback, reduced fruit production, and eventually tree death. Control strategies focus on pruning out infected wood well below the visible staining, protecting fresh wounds with wound paint, and avoiding pruning during damp conditions when spore counts are high.

• Sterilizing pruning tools with alcohol or bleach
• Prompt removal of dead or dying branches
• Applying protective sealants to pruning wounds
• Maintaining tree vigor through proper fertilization