Cherry leaf spot

Cherry leaf spot, caused by the fungus Coccomyces prunophorae (syn. Blumeriella jaapii), is a devastating disease affecting stone fruit trees. It is particularly notorious for causing premature defoliation, which severely stresses the tree's health and productivity.

The primary hosts of this pathogen include cherries, plums, apricots, and other Prunus species. While the disease primarily targets the foliage, in cases of high humidity and heavy infestation, it can also manifest as lesions on fruit stalks and young green stems.

Initial symptoms include the emergence of tiny purple or reddish-brown spots on the upper leaf surface. These spots eventually enlarge and merge. Under moist conditions, a white or pinkish fungal mass, consisting of conidia, appears on the underside of the leaves, corresponding to the spots.

The fungus thrives in warm, wet weather. The pathogen overwinters in infected leaves on the ground. During spring, when temperatures rise and rain occurs, spores are released and splashed onto the leaves by wind and water, triggering the infection cycle.

The economic impact of cherry leaf spot is severe due to the loss of photosynthetic area. Premature leaf drop leads to poor fruit quality, stunted growth, and a dramatic reduction in winter hardiness. Infected trees are highly susceptible to freeze damage and may eventually die if the disease is not controlled for several seasons.

Effective management and control strategies include:

• Sanitation: Raking and removing fallen leaves in autumn to eliminate the primary source of overwintering inoculum.
• Fungicide applications: Using copper-based or systemic fungicides during the early spring and post-harvest periods.
• Pruning: Maintaining an open canopy structure to promote better air circulation and faster drying of leaves.
• Monitoring: Scouting the orchard for early signs of lesions to initiate chemical control before the outbreak becomes widespread.