Scab

The host range for scab is extensive, impacting various horticultural and agricultural crops worldwide. Common manifestations include apple scab (caused by Venturia inaequalis), which significantly damages orchard yields, and common potato scab (caused by Streptomyces scabies), which affects tubers in soils with high pH. Other vegetables and ornamental plants are also susceptible to specific pathotypes of these organisms.

Symptoms typically begin as small, discolored spots that gradually enlarge, becoming rough, scabby, or cracked. On leaves, these spots may lead to defoliation, while on fruits and tubers, they cause surface disfigurement. The presence of these scabs reduces the marketability of the produce, as consumers associate these blemishes with lower quality, even if the internal tissue remains edible.

The development of scab is highly dependent on environmental conditions. High humidity, cool to moderate temperatures, and prolonged periods of leaf wetness are critical for the germination and spread of fungal spores. In the case of soil-borne scab, dry conditions during the early stages of tuber development combined with neutral or alkaline soil conditions create the most favorable environment for pathogen proliferation.

The economic impact of scab is significant, often resulting in high cull rates and reduced storage longevity. Effectively managing the disease requires an integrated approach to avoid total crop failure. Recommended control measures include:

• Planting resistant or tolerant cultivars;
• Implementing strict crop rotation practices;
• Maintaining proper soil pH levels based on the specific crop requirements;
• Removing and destroying infected plant debris to reduce spore load;
• Applying preventive fungicide sprays during high-risk growth stages.