Leptosphaeria canker and fruit rot

Leptosphaeria canker and fruit rot, caused by the fungal pathogen Diapleella coniothyrium, is a persistent fungal disease that significantly impacts bark tissue and fruit quality in various woody plants. The pathogen thrives in necrotic tissues and is notorious for its ability to persist in plant debris for extended periods, serving as a constant threat to orchard health.

While the disease affects numerous species, domestic apple (Malus domestica) is a primary host for this fungus. The pathogen acts as an opportunistic invader, primarily entering the host through physical wounds, pruning cuts, sunscald areas, frost cracks, or points of damage caused by various insect pests that breach the outer bark layers.

The characteristic symptoms include depressed, necrotic lesions on branches and stems, which often expand to girdle the woody parts, leading to dieback. On fruits, the disease typically manifests as a rapid-spreading decay that turns the flesh soft and discolored. Over time, the surface of these lesions produces dark fruiting structures (pycnidia) containing fungal spores.

Favorable conditions for the development and spread of Diapleella coniothyrium include high ambient humidity, prolonged periods of leaf wetness, and moderate temperatures. The fungus disseminates its spores primarily through splashing rain, wind-blown water droplets, and contaminated tools used during routine maintenance and pruning operations.

The damage caused by this pathogen is multifaceted, ranging from the loss of individual fruit clusters to the death of entire scaffold branches. If left unmanaged, the canker infection weakens the tree's overall vigor, reduces fruit yields significantly, and shortens the economic lifespan of the orchard by creating entry points for secondary pathogens and wood-boring insects.

• Regular pruning of infected branches, cutting well into healthy wood.
• Prompt sealing of pruning wounds with appropriate pruning sealers or fungicides.
• Sterilization of pruning tools between trees to prevent cross-contamination.
• Application of protective copper-based sprays during the dormant season.
• Effective insect control to minimize entry points for fungal spores.