Alternaria leaf blight of Cucurbits

Alternaria cucumerina

Causal Agent: Alternaria cucumerina is a fungal pathogen responsible for causing Alternaria leaf spot, a common disease affecting cucurbit crops such as cucumbers, melons, and pumpkins.

Symptoms:

  1. Leaf Lesions:

    • Circular Lesions: The disease manifests as small, circular lesions on the leaves.
    • Dark Centers: Lesions often have dark centers with concentric rings, creating a distinctive target-like appearance.

  2. Lesion Development:

    • Lesions Expand: Over time, the lesions can expand and coalesce, covering larger areas of the leaf.
    • Yellowing: Yellowing of the tissue surrounding the lesions may occur.

  3. Fruit Symptoms:

    • Fruit Lesions: In severe cases, lesions can also appear on the fruit, affecting the marketability and quality.
    • Sunken Spots: Lesions on fruit may be sunken and have a corky texture.

  4. Spore Production:

    • Dark Spore Structures: Dark spore structures, called conidia, may develop within the lesions.

Identification:

  1. Circular Lesions: Small, circular lesions on leaves with a target-like appearance.
  2. Dark Spore Structures: Presence of dark spore structures within lesions.

Conditions Favoring Disease:

  1. Humid Conditions: Alternaria species thrive in humid environments, and disease incidence increases under high humidity.
  2. Warm Temperatures: Warmer temperatures contribute to the rapid development and spread of the disease.

Management:

  1. Fungicides:

    • Copper-based Fungicides: Copper-based fungicides can be used as a preventive measure.
    • Systemic Fungicides: Systemic fungicides may be applied for curative control.
    • Regular Applications: Application intervals should be based on disease severity and environmental conditions.

  2. Cultural Practices:

    • Crop Rotation: Practice crop rotation to reduce the buildup of inoculum in the soil.
    • Sanitation: Remove and destroy infected plant debris to minimize the source of spores.
    • Proper Spacing: Ensure proper spacing between plants for good air circulation.

  3. Resistant Varieties:

    • Plant Resistant Cultivars: Consider planting cultivars that have been bred for resistance to Alternaria leaf spot.

  4. Monitoring:

    • Regular Field Inspection: Regularly inspect plants for early signs of the disease.
    • Weather Monitoring: Be vigilant during periods of high humidity and warm temperatures.

Note: Integrated disease management, combining chemical control with cultural practices, is often the most effective approach.