Apple scab

Apple scab is a destructive plant disease caused by fungi of the genus Venturia. Specifically, Venturia inaequalis is the primary pathogen responsible for the disease in apple trees, while Venturia pyrina typically affects pear trees. It is considered one of the most economically significant fungal infections in commercial and home orchards worldwide.

The disease primarily attacks the foliage, blossoms, and fruits of pome fruits. The pathogen overwinters in infected plant debris, specifically fallen leaves. In early spring, during wet weather, the fungus releases spores that are carried by wind or rain splashes to the new growth, initiating the primary infection cycle of the season.

Symptoms initially appear as small, olive-green to brown spots on the underside of leaves. As the infection progresses, these spots expand, darken, and develop a velvety appearance. On fruits, the lesions become corky, leading to fruit cracking, stunted growth, and significant deformity, which renders the harvest unsuitable for commercial sale.

Environmental conditions play a critical role in the severity of the outbreak. The fungus thrives in cool, wet environments where leaf surfaces remain moist for extended periods. High humidity, frequent rainfall, and poor air circulation within the tree canopy significantly increase the rate of spore germination and overall disease spread.

Managing apple scab requires an integrated pest management approach to minimize damage:

• sanitation practices such as removing and destroying fallen leaves;
• pruning to improve canopy airflow and light penetration;
• application of protective copper-based or systemic fungicides during critical infection periods;
• planting resistant or tolerant cultivars to reduce dependence on chemical controls.