Coccomyces vilis

The causative agent of this disease is the fungus Coccomyces vilis (synonym Blumeriella jaapii), which is responsible for one of the most destructive diseases in stone fruit orchards, particularly in cherry and sour cherry plantations.

The disease primarily affects plants within the Rosaceae family. While cherries and sour cherries are the most common hosts, the fungus can also infect plums, apricots, and various wild species of Prunus, making it a persistent challenge for commercial and home growers alike.

Symptoms appear early in the growing season as small, dark purple or reddish spots on the leaf surface. As the infection progresses, these spots expand, often merging, and a characteristic whitish-pink fungal growth appears on the underside of the leaves, eventually leading to chlorosis and premature defoliation.

Environmental conditions such as high humidity and frequent rainfall are essential for the dispersal of ascospores from overwintering infected leaves. The fungus spreads rapidly during warm, wet spring weather, moving from debris on the orchard floor to healthy leaves and new green shoots.

The economic impact of this disease is significant, primarily due to the severe weakening of the trees. Early leaf fall disrupts photosynthesis, preventing the accumulation of winter reserves, which leads to reduced cold hardiness, susceptibility to secondary infections, and reduced fruit quality or total loss of yield.

• Rigorous sanitation by removing and composting or burning fallen leaves.
• Applying fungicides during the pre-blossom and post-harvest stages.
• Maintaining proper spacing between trees to ensure adequate airflow.
• Promoting orchard health through balanced fertilization and pruning.