Anthracnose of Lettuce

Marssonina panattoniana

Causal Agent: Marssonina panattoniana is a fungal pathogen responsible for causing Marssonina leaf spot, a common disease affecting apple trees.

Symptoms:

  1. Leaf Lesions:

    • Circular Lesions: Marssonina leaf spot lesions are typically small, circular spots on the upper side of leaves.
    • Dark Brown to Black Color: Lesions often have a dark brown to black coloration.
    • Yellowing Surrounding Lesions: Yellowing of the tissue surrounding the lesions may occur.

  2. Lesion Development:

    • Enlargement of Lesions: As the disease progresses, lesions may enlarge and coalesce, leading to extensive defoliation.
    • Concentric Rings: Lesions may display concentric rings, giving them a target-like appearance.

  3. Fruit Symptoms:

    • Fruit Lesions: In severe cases, the disease may also affect fruit, causing lesions and affecting overall fruit quality.

  4. Spore Production:

    • Conidia Formation: The fungus produces conidia (asexual spores) in structures within the lesions.

Identification:

  1. Circular Lesions: Small, circular spots with a dark brown to black color on the upper side of leaves.
  2. Yellowing: Yellowing of tissue around lesions, particularly as lesions enlarge.

Conditions Favoring Disease:

  1. Warm and Humid Conditions: Marssonina leaf spot thrives in warm and humid environments.
  2. Rain or Irrigation: Moisture on leaves from rain or irrigation facilitates spore dispersal and infection.

Management:

  1. Fungicides:

    • Protective Fungicides: Regular application of fungicides during the growing season, especially during periods conducive to disease development.
    • Cultural Practices: Properly time fungicide applications based on the apple tree's growth stage and weather conditions.

  2. Cultural Practices:

    • Leaf Removal: Remove and destroy infected leaves to reduce inoculum.
    • Proper Pruning: Prune trees to improve air circulation and reduce humidity within the canopy.
    • Sanitation: Remove and destroy fallen leaves to minimize overwintering spores.

  3. Resistant Varieties:

    • Plant Resistant Cultivars: Consider planting apple varieties that show resistance or tolerance to Marssonina leaf spot.

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