Angular leaf spot of persimmon

The causative agent of this disease is the fungus Plurivorosphaerella nawae (formerly classified as Mycosphaerella nawae). This fungal pathogen is known to cause severe leaf drop, which significantly weakens the host tree and affects its overall physiological condition and resilience during the winter months.

The disease primarily affects the Asian persimmon (Diospyros kaki). It is a significant concern for both commercial orchards and home gardens where this specific cultivar is grown, particularly in regions with high humidity levels and frequent rainfall during the active growing season.

The clinical symptoms of the disease appear as small, dark brown or black angular spots on the leaves, which are typically bounded by leaf veins. As the disease progresses, these spots enlarge and merge, resulting in extensive tissue necrosis. This eventually triggers premature defoliation, which can occur well before the natural leaf-fall period.

Favorable conditions for the development and spread of the pathogen include high atmospheric humidity, rainfall events that splash spores onto foliage, and moderate to warm temperatures. The fungus overwinters in the fallen leaves as perithecia, which act as the primary inoculum source for the subsequent spring infection cycle.

The economic impact of Plurivorosphaerella nawae is substantial, as it leads to a significant loss of leaf area, reducing the photosynthetic capacity of the tree. This stress results in poor fruit development, fruit drop, and depleted reserves in the branches, which significantly increases the risk of winter kill and reduces the tree's future productive capacity.

Management and prevention strategies include:

• Strict sanitation practices, such as raking and destroying all fallen leaves in autumn to eliminate the overwintering inoculum.
• Applying preventative fungicide treatments, such as copper-based sprays or systemic fungicides, early in the growing season.
• Maintaining optimal tree health through balanced fertilization and correct pruning to improve air circulation within the canopy.
• Monitoring for early symptoms to apply timely chemical interventions before the epidemic spreads.