Blister disease of pear

Blister disease of pear is caused by the fungus Coniothecium chromatosporum (also known as Phaeocytostroma sacculum). This pathogen acts as a necrotrophic parasite, primarily affecting the protective tissues of the tree, which can lead to localized necrosis and severe structural damage to the woody parts.

The primary host for this pathogen is the common pear (Pyrus communis). The disease predominantly affects the bark of the trunk and primary scaffolding branches, making it a critical concern for both young orchards and mature, high-yielding pear trees.

The disease is characterized by the formation of numerous small blisters or pustules beneath the outer layer of the bark. As the disease progresses, these blisters rupture, releasing a mass of black spores that often look like a sooty coating. This results in the localized death of the cortex, leading to visible cracks, lesions, and the eventual decay of the affected bark tissue.

Development and spread of the fungus are heavily dependent on environmental stress factors, particularly bark damage caused by winter sunscald or frost cracks. Moist conditions during the growing season facilitate the mass production of spores, which are then disseminated by wind, rain splashes, and human activities, including pruning with contaminated tools.

Effective management requires a combination of cultural and chemical strategies. Key prevention and control measures include:

• Prompt removal and destruction of infected branches to reduce inoculum.
• Disinfecting pruning tools between trees to prevent cross-contamination.
• Application of copper-based fungicides to seal wounds and protect bark.
• Whitewashing trunks to mitigate the risk of sunscald, which serves as a primary entry point for the fungus.
• Maintaining tree vigor through balanced fertilization and appropriate irrigation.