Anthracnose of Pistachio

Colletotrichum acutatum. C. acutatum

Causal Agent: Anthracnose in pistachios is primarily caused by the fungus Colletotrichum gloeosporioides.

Symptoms:

  1. Leaf Lesions:

    • Circular Lesions: Anthracnose lesions on pistachio leaves are typically circular and may vary in size.
    • Dark Centers: Lesions often have dark brown to black centers.
    • Reddish to Dark Margins: The margins of the lesions may appear reddish to dark in color.

  2. Twig and Shoot Lesions:

    • Lesions on Twigs: Twigs and shoots may develop lesions, affecting the overall health of the tree.

  3. Nut Lesions:

    • Lesions on Nuts: Anthracnose can affect pistachio nuts, causing sunken lesions with dark centers.
    • Conidia Formation: The fungus produces conidia (asexual spores) within the lesions.

  4. Reduced Yield and Quality:

    • Necrosis: Severe anthracnose can lead to necrosis and premature drop of leaves, twigs, and nuts.
    • Reduced Nut Quality: Infected nuts may exhibit reduced quality and market value.

Identification:

  1. Circular Lesions: Circular lesions with dark centers on leaves, twigs, and nuts.
  2. Reddish to Dark Margins: Reddish to dark margins around the lesions, particularly on leaves.

Conditions Favoring Disease:

  1. Warm and Humid Conditions: Anthracnose thrives in warm and humid environments.
  2. Rain or Irrigation: Moisture on leaves, twigs, and nuts from rain or irrigation facilitates spore dispersal and infection.

Management:

  1. Resistant Varieties:

    • Plant Resistant Cultivars: Choose pistachio varieties that show resistance or tolerance to Colletotrichum gloeosporioides.

  2. Cultural Practices:

    • Crop Sanitation: Remove and destroy infected plant material, including fallen leaves and nuts.
    • Proper Pruning: Prune trees to improve air circulation and reduce humidity within the canopy.
    • Avoid Overhead Irrigation: Minimize prolonged leaf wetness by using drip or furrow irrigation.

  3. Fungicides:

    • Protective Fungicides: Regular application of fungicides during the growing season, especially during periods conducive to disease development.

  4. Post-Harvest Practices:

    • Proper Harvesting: Implement proper harvesting practices to reduce physical damage to nuts, which can provide entry points for the pathogen.

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