Mycosphaerella horii

Mycosphaerella horii is a fungal pathogen classified within the family Mycosphaerellaceae. It is the causal agent of the angular leaf spot disease of persimmon (Diospyros kaki). The asexual stage of this fungus is widely recognized in plant pathology as Cercospora kaki.

The primary host for this pathogen is the Oriental persimmon. The disease is characterized by the appearance of angular, brown-to-black lesions on the leaves. As the disease progresses, these lesions merge, causing the leaves to turn yellow and abscise prematurely, which disrupts the tree's vital physiological functions.

The life cycle of the pathogen is centered on the survival of mycelia and pseudothecia within infected leaf litter during the winter. In the spring, primary infections are initiated by ascospores released from these overwintered structures. These spores are disseminated by wind and rain splashes to the emerging young foliage of the host tree.

Conditions favoring the development and spread of Mycosphaerella horii include high relative humidity, frequent rain, and moderate temperatures. In neglected orchards with dense foliage, the microclimate becomes highly conducive to the pathogen's rapid proliferation, leading to secondary infection cycles that can devastate the canopy throughout the growing season.

The economic impact is significant due to reduced photosynthesis caused by defoliation. This leads to diminished fruit size, lower sugar content, and an overall lack of tree vigor. Weakened trees exhibit poor cold tolerance, making them highly susceptible to winter injury and reducing the potential for successful harvests in subsequent years.

• Remove and destroy fallen leaves to reduce the primary inoculum source.
• Prune trees annually to ensure adequate sunlight and air circulation within the canopy.
• Apply copper-based fungicides during the dormant season to eliminate overwintering spores.
• Implement a preventive spray program with systemic fungicides during the active growth period.
• Maintain optimal tree health through balanced fertilization and stress management.