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:
- Leaf Lesions: The disease typically starts as small, dark brown to black lesions on leaves.
- Target Spot Appearance: Lesions may have a concentric ring or "target spot" appearance.
- Lesion Enlargement: As the disease progresses, lesions can enlarge and coalesce, leading to extensive damage.
- Yellowing and Necrosis: Surrounding the lesions, there may be yellowing of the tissue, and severe infections can cause necrosis.
- Spore Production: In humid conditions, the fungus may produce dark spores, giving the lesions a fuzzy appearance.
Identification:
- Leaf Inspection: Regularly inspect plants for characteristic lesions.
- Target Spot Appearance: Recognize the concentric ring pattern on lesions.
Disease Cycle:
- Survival: The fungus can survive on infected plant debris, seeds, or in the soil.
- Spore Production: Spores are produced on infected plant material, and wind or rain can spread them to healthy plants.
- Infection: Spores germinate and penetrate plant tissues, initiating infection.
Management:
Cultural Practices:
- Crop Rotation: Rotate crops to break the disease cycle and reduce inoculum in the soil.
- Sanitation: Remove and destroy infected plant debris to reduce overwintering sources.
- Proper Spacing: Ensure proper plant spacing to improve air circulation.
Fungicide Application:
- Foliar Fungicides: Application of fungicides, especially during periods of high disease pressure, can help manage Alternaria leaf spot.
Resistant Varieties:
- Plant Resistant Varieties: Choose plant varieties that are resistant or less susceptible to Alternaria alternata.
Regular Monitoring:
- Scouting for Symptoms: Regularly monitor plants for early symptoms of Alternaria leaf spot, especially during conditions conducive to disease development.
Weather Considerations:
- Humidity Management: Minimize leaf wetness by avoiding overhead irrigation, especially during the evening.







