Sooty mold

Alternaria alternata

Alternaria alternata:

Alternaria alternata is a widespread fungal pathogen that affects a variety of plants, causing diseases collectively known as Alternaria leaf spot or blight. Here's an informative description:

Hosts:

  • Alternaria alternata can infect a wide range of plants, including fruits, vegetables, ornamentals, and field crops.

Symptoms:

  1. Leaf Lesions: The disease typically starts as small, dark brown to black lesions on leaves.
  2. Target Spot Appearance: Lesions may have a concentric ring or "target spot" appearance.
  3. Lesion Enlargement: As the disease progresses, lesions can enlarge and coalesce, leading to extensive damage.
  4. Yellowing and Necrosis: Surrounding the lesions, there may be yellowing of the tissue, and severe infections can cause necrosis.
  5. Spore Production: In humid conditions, the fungus may produce dark spores, giving the lesions a fuzzy appearance.

Identification:

  1. Leaf Inspection: Regularly inspect plants for characteristic lesions.
  2. Target Spot Appearance: Recognize the concentric ring pattern on lesions.

Disease Cycle:

  1. Survival: The fungus can survive on infected plant debris, seeds, or in the soil.
  2. Spore Production: Spores are produced on infected plant material, and wind or rain can spread them to healthy plants.
  3. Infection: Spores germinate and penetrate plant tissues, initiating infection.

Management:

Cultural Practices:

  1. Crop Rotation: Rotate crops to break the disease cycle and reduce inoculum in the soil.
  2. Sanitation: Remove and destroy infected plant debris to reduce overwintering sources.
  3. Proper Spacing: Ensure proper plant spacing to improve air circulation.

Fungicide Application:

  1. Foliar Fungicides: Application of fungicides, especially during periods of high disease pressure, can help manage Alternaria leaf spot.

Resistant Varieties:

  1. Plant Resistant Varieties: Choose plant varieties that are resistant or less susceptible to Alternaria alternata.

Regular Monitoring:

  1. Scouting for Symptoms: Regularly monitor plants for early symptoms of Alternaria leaf spot, especially during conditions conducive to disease development.

Weather Considerations:

  1. Humidity Management: Minimize leaf wetness by avoiding overhead irrigation, especially during the evening.