Algal Leaf Spot Disease is a common problem that affects many plants, including guava. This disease is caused by the alga Cephaleuros, which can survive on plant debris and other surfaces for extended periods. The pathogen spreads through wind and water, and it can cause significant damage to plant health and productivity. Effective management of this disease requires an understanding of its biology and life cycle, as well as the implementation of appropriate control measures.
Algal Leaf Spot Disease Management in Guava
The Causal Organism of Algal Leaf Spot Disease
The causal organism of Algal Leaf Spot Disease is a type of alga known as Cephaleuros. This pathogen is a member of the green algae family and can infect thick-leafed plants during the summer when rain spreads the pathogen. The colonies of Cephaleuros can survive on fallen leaves for a time and spread to growing leaves, causing the formation of brownish-green to soft black spots.
The Disease cycle of Algal Leaf Spot Disease
- Infection: The disease starts when the alga infects immature guava leaves during the early spring flush. The alga enters the leaf tissue through natural openings or wounds.
- Lesion formation: Once inside the leaf tissue, the alga starts to grow and multiply, causing the formation of minute, shallow brown velvety lesions on the leaves. These lesions can appear on the leaf tips, margins, or areas near the mid-vein. The lesions are 2-3 mm in diameter as the disease progresses.
- Sporulation: The alga produces spores within the lesions, dispersed by wind, water, or insects to other parts of the plant or nearby plants.
- Secondary infections: When the spores land on susceptible tissues, such as immature fruits or leaves, they can cause secondary infections and start new lesions.
- Disease development: As the disease progresses, the lesions on leaves may vary from tiny spots to big patches, which may be crowded or scattered. On unripe fruits, the lesions are nearly black. As fruits grows, lesions get lowered and get cracked frequently on older blemishes due to the enlargement of fruits. Lesions are usually smaller than leaf spots and are darkish green to brown or black.
Causes/Conditions Favorable for Algal Leaf Spot Disease Spread in the Field.
- Wet and humid conditions: The disease thrives in moist environments, and prolonged periods of high humidity and rainfall can create conditions ideal for its growth and spread.
- Poor air circulation: Limited air movement and ventilation can create a microclimate that favors the development and spread of the disease.
Symptoms of Algal Leaf Spot Disease
- Minute, shallow brown velvety lesions appear on immature guava leaves during the early spring flush.
- The lesions are usually found on leaf tips, margins, or areas near the mid-vein of the leaf.
- As the disease progresses, the lesions enlarge to 2-3 mm in diameter and may vary from specks to big patches that can be crowded or scattered.
- On immature fruits, the lesions are nearly black.
- As the fruits enlarge, the lesions become sunken and frequently cracked on older blemishes.
- The fruit lesions are usually smaller than those on leaves and can be darkish green to brown or black.