Pear scab

Pathogen and Disease Type. Pear scab is a significant fungal disease caused by the ascomycete Venturia pyrina. It is a host-specific pathogen that targets pear trees, leading to severe damage in orchards. The fungus overwinters in dead leaves on the ground or within lesions on twigs, producing spores that initiate infection when environmental conditions become favorable in early spring.

Affected Crops. The disease primarily affects pear trees (Pyrus species). All aerial parts of the tree, including leaves, buds, blossoms, fruits, and young twigs, are susceptible. Young tissue is particularly prone to infection, but as the season progresses, the fungus can infect even developing fruits, causing significant yield losses and reducing fruit marketability.

Symptoms and Signs. Infection typically begins as small, olive-brown spots on the underside of leaves. As the fungus develops, these spots become velvety with spore production. On fruits, the disease appears as dark, corky scabs that often lead to cracking and disfigurement. Twigs may show small blisters or pustules, which eventually rupture to release spores.

Conditions for Development. Venturia pyrina thrives in cool, wet weather conditions. Prolonged leaf wetness and moderate temperatures (around 15-20°C) are critical for the germination and spread of spores. Orchards with poor airflow, dense canopies, or high humidity levels are at a much higher risk of experiencing severe disease outbreaks.

Control and Prevention. Effective management of pear scab requires an integrated approach to reduce the inoculum pressure in the orchard. Recommended actions include:

• Removing and destroying fallen leaves in the autumn to eliminate overwintering sites.
• Pruning trees to improve light penetration and air circulation within the canopy.
• Applying protective or systemic fungicides at key phenological stages.
• Planting pear varieties that show resistance or tolerance to scab.