Potato gangrene

Phoma exigua

Appearance:

Leaf Symptoms:

  1. Lesions: Phoma exigua typically causes circular to irregular lesions on the leaves of host plants.
  2. Color Changes: Lesions may start as water-soaked and progress to tan or light brown, often with a dark brown margin.
  3. Concentric Rings: Mature lesions may exhibit concentric rings, giving them a distinctive appearance.

Stem Symptoms:

  1. Stem Cankers: In addition to affecting leaves, Phoma exigua can cause cankers on stems.
  2. Lesion Expansion: Cankers may expand and girdle the stem, leading to wilting and dieback.

Identification:

  1. Leaf and Stem Inspection: Regularly inspect leaves and stems for the characteristic lesions and cankers caused by Phoma exigua.
  2. Lesion Characteristics: Look for circular to irregular lesions with a water-soaked appearance that progress to tan or light brown. Mature lesions may show concentric rings.
  3. Stem Cankers: Check for cankers on stems, especially if wilting and dieback symptoms are observed.

Management:

  1. Resistant Varieties:

    • Plant Resistant Varieties: Utilize crop varieties that are bred for resistance or tolerance to Phoma exigua when available.

  2. Crop Rotation:

    • Rotate Crops: Implement a crop rotation strategy to reduce the buildup of Phoma exigua in the soil.

  3. Fungicide Application:

    • Fungicidal Sprays: Application of fungicides, especially those effective against Phoma exigua, can be part of an integrated disease management strategy. Consult with local agricultural experts for recommended fungicides and application schedules.

  4. Sanitation:

    • Remove Infected Debris: Promptly remove and destroy infected plant debris, including leaves and stems, to reduce the inoculum source.

  5. Cultural Practices:

    • Proper Plant Spacing: Ensure proper spacing between plants to improve air circulation and reduce humidity, creating less favorable conditions for the fungus.
    • Avoid Overhead Irrigation: Minimize moisture on plant surfaces by using drip irrigation or watering at the base of the plants.

  6. Regular Monitoring:

    • Scouting for Symptoms: Regularly monitor crops for early symptoms of Phoma exigua, especially during conditions conducive to disease development.