Anthracnose of Beans

Colletotrichum lindemuthianum

Causal Agent: Colletotrichum lindemuthianum is a fungal pathogen responsible for causing anthracnose in common beans (Phaseolus vulgaris). Anthracnose is a significant disease affecting bean crops worldwide.

Symptoms:

  1. Leaf Lesions:

    • Circular Lesions: Anthracnose lesions on leaves are typically circular with a dark brown to black color.
    • Concentric Rings: Lesions may show concentric rings as they expand.
    • Water-Soaked Appearance: Lesions can appear water-soaked in the early stages.

  2. Pod Lesions:

    • Lesions on Pods: Pods may develop sunken lesions with a dark appearance.
    • Conidia Formation: The fungus produces conidia in acervuli within the lesions.

  3. Stem Lesions:

    • Lesions on Stems: Stems may also be affected, leading to lesions that can girdle the stem.

  4. Seedborne Infection:

    • Infected Seeds: The pathogen can be seedborne, leading to infected seeds.
    • Reduced Seed Quality: Infected seeds may exhibit reduced germination and seedling vigor.

Identification:

  1. Circular Lesions: Circular, dark brown to black lesions on leaves, pods, and stems.
  2. Concentric Rings: Lesions may show concentric rings as they expand.

Conditions Favoring Disease:

  1. Humid Conditions: Anthracnose is favored by high humidity and warm temperatures.
  2. Rain or Irrigation: Moisture on leaves and pods from rain or irrigation facilitates spore dispersal and infection.

Management:

  1. Resistant Varieties:

    • Plant Resistant Cultivars: Use bean varieties that exhibit resistance or tolerance to Colletotrichum lindemuthianum.

  2. Cultural Practices:

    • Crop Rotation: Rotate bean crops with non-host crops to reduce inoculum.
    • Sanitation: Remove and destroy infected plant material, including crop residues.
    • Proper Spacing: Ensure adequate spacing between plants for good air circulation.

  3. Fungicides:

    • Protective Fungicides: Application of fungicides may be considered, especially during periods conducive to disease development.

  4. Seed Treatment:

    • Seed Treatment: Treat bean seeds with fungicides to reduce the potential for seedborne infection.

Note: Integrated disease management, combining cultural practices, resistant varieties, and, if necessary, fungicides, is often the most effective approach.

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