Pezicula bark canker

Pezicula corticola is a fungal pathogen responsible for a type of bark canker that affects various fruit-bearing trees, particularly pome fruits like apples and pears. This fungus primarily attacks the outer layers of the bark and the underlying cambium, leading to the development of necrotic lesions that disrupt the tree's vascular transport system.

The disease usually infects the plant through wounds or points of weakness, such as pruning cuts, frost cracks, or damage caused by pests. Once inside, the fungus colonizes the living tissue, causing the bark to sink, discolour, and eventually detach from the wood, which can lead to the wilting and eventual death of individual branches or even entire trees if the main trunk is girdled.

Diagnostic symptoms include the formation of localized sunken areas on the bark. During humid conditions, small, disc-shaped fruiting bodies, known as apothecia, may emerge from the center of these lesions. They are typically light brown to cream-coloured. As the disease progresses, the bark may crack or peel away, revealing the underlying woody tissue, which often shows signs of decay.

The spread of the fungus is heavily dependent on moisture. Rainfall splashes spores from existing cankers onto healthy bark, and wind can carry them to neighbouring trees. Warm and damp spring or autumn weather creates ideal conditions for the germination of spores and the establishment of new infection sites. The pathogen can survive for long periods in infected bark, making it a persistent threat in orchards.

Management of this disease relies heavily on sanitation and preventive measures. Infected branches must be pruned back to healthy wood, with tools thoroughly disinfected between cuts to prevent cross-contamination. Preventive applications of copper-based fungicides during the dormant season are standard practice. Furthermore, maintaining tree vigour through proper fertilization and pest control reduces the tree's susceptibility to opportunistic fungal attacks.