Alternaria blight

Pathogen and disease type. The pathogen Alternaria penicillata is a fungus belonging to the order Pleosporales. It causes Alternaria blight, a significant fungal disease that affects various plant parts, including leaves, stems, and seeds, often leading to rapid necrosis and tissue degradation during the growing season.

Affected crops. This pathogen has a broad host range, primarily infecting small grains such as wheat and barley. It also poses a serious threat to various vegetable crops and oilseeds. The fungus is frequently seed-borne, meaning it can be transmitted through infected seed lots, causing damping-off and poor emergence in subsequent crop cycles.

Symptoms and signs. Typical symptoms include dark brown or black lesions on the leaves, often characterized by concentric zones. A dark, sooty, or olive-green velvety layer of spores is visible on the surface of the lesions during humid conditions. Infected stems and heads show discoloration, and the grain may become shriveled, discolored, or covered with a fungal mat.

Development and spread. Alternaria penicillata thrives in warm, humid environments. It survives in infected crop debris, the soil, and on seeds. Sporulation and infection are significantly enhanced by prolonged periods of leaf wetness and temperatures between 18°C and 25°C, allowing the disease to spread rapidly through fields under favorable climatic conditions.

Harmfulness and control measures. The disease causes significant yield losses, reduces grain weight, and impairs seed germination. Effective management strategies involve:

• Using certified, disease-free seed lots.
• Applying systemic fungicide seed treatments before sowing.
• Implementing crop rotation to break the pathogen's life cycle.
• Applying foliar fungicides at the first sign of symptoms during the growing season.