Apple bark rot

Pezicula malicorticus (syn. Neofabraea malicorticis) is a fungus belonging to the class Leotiomycetes, recognized as a primary pathogen causing the surface bark canker (bull's eye rot) on apple trees. This pathogen significantly impacts the vitality of trees and the quality of harvested fruits, posing a persistent challenge to commercial apple production.

The fungus manifests as distinct circular or oval cankers on the bark, which can eventually girdle limbs and lead to dieback. On the surface of these cankers, the pathogen produces small, disc-shaped fruiting bodies known as apothecia. Beyond the bark, the fungus is known to cause post-harvest storage rots, manifesting as depressed, brownish lesions on the fruit surface, often with a bitter taste.

The disease cycle of Pezicula malicorticus is highly dependent on environmental moisture. The fungus overwinters in the infected bark and canker tissues. During cool, wet weather, particularly in late autumn or spring, it produces spores (conidia and ascospores) that are disseminated by rain splash to healthy bark or developing fruits. Penetration occurs through lenticels, pruning cuts, or minor mechanical injuries.

The economic impact is twofold: it reduces the productivity of the tree canopy through limb death and significantly decreases the market value of the harvest due to storage rot. Persistent infections weaken the tree, making it more susceptible to other opportunistic pathogens and environmental stresses, eventually necessitating the removal of entire trees.

• Rigorous pruning to remove infected wood and improve air circulation.
• Prompt sanitation by burning or burying infected plant material.
• Application of copper-based fungicides during the dormant season.
• Protection of pruning wounds with appropriate sealant products.
• Careful monitoring of fruit in storage to prevent secondary outbreaks.

Effective control requires an integrated approach focusing on orchard hygiene and timely chemical applications. Preventing the spread of spores during wet periods is crucial for minimizing new infections. By maintaining optimal canopy density and ensuring that trees are not stressed, growers can significantly reduce the vulnerability of their orchards to this damaging fungal pathogen.