Parasitic algae

Cephaleuros virescens

Cephaleuros virescens is a green parasitic alga that causes a plant disease known as algal leaf spot or green scurf. This pathogen affects a variety of plants, including tropical and subtropical trees and shrubs. It's particularly known to impact ornamental plants, such as camellias, azaleas, and citrus trees. Here is an informative description of Cephaleuros virescens, including its appearance, identification, and management:

Cephaleuros virescens:

Appearance: Cephaleuros virescens is a green alga that forms irregularly shaped, powdery green spots on the leaves, stems, and fruits of infected plants. These spots can vary in size and color from green to red or brown. As the alga matures, it may produce structures called sporangia, which can give the affected plant parts a fuzzy or velvety appearance.

Identification:

  1. Green Spots: Look for irregular green spots on the surfaces of leaves, stems, and fruits.
  2. Powdery Appearance: The spots may appear powdery or velvety, especially as the alga produces sporangia.
  3. Color Variation: The color of the spots can range from green to red or brown.
  4. Fuzzy Growth: Mature infections may exhibit a fuzzy or velvety growth due to the presence of sporangia.

Management:

  1. Fungicide Application:

    • Copper-Based Fungicides: Copper-based fungicides are commonly used to manage Cephaleuros virescens infections. Application should be timed according to the specific recommendations for the affected plant species.

  2. Pruning and Removal of Infected Tissues:

    • Prune Infected Parts: Prune and remove infected leaves, stems, or fruits to reduce the inoculum source and slow down the spread of the alga.
    • Proper Disposal: Dispose of the pruned material properly to avoid further contamination.

  3. Cultural Practices:

    • Improve Air Circulation: Ensure proper spacing and pruning to improve air circulation around plants, which can create less favorable conditions for algal growth.
    • Avoid Overhead Irrigation: Minimize moisture on plant surfaces by using drip irrigation or watering at the base of the plants.

  4. Biological Control:

    • Introduction of Natural Predators: In some cases, the introduction of natural predators or biological control agents may help manage algal leaf spot.

  5. Regular Monitoring:

    • Scouting for Symptoms: Regularly monitor plants for the characteristic symptoms of algal leaf spot, especially during conditions favorable for algal growth.