Why in News?
Leaf spot diseases are recently in the news because of major outbreaks in Arecanut plantations in Southern India and a series of scientific breakthroughs regarding pathogen co-infection in staple crops like wheat.
What is it?
- Definition: A broad group of plant diseases caused by fungi (85% of cases), bacteria, or viruses that produce localized lesions on foliage.
- Primary Pathogens:
- Fungi: Cercospora, Septoria, Alternaria, and the newly identified Colletotrichum cigarro.
- Bacteria: Common in stone fruits (cherry, plum) and vegetables like cucumbers.
- Viruses: Often lead to "mosaic" patterns and ring spots rather than simple lesions.
Key Symptoms
- Early Signs: Small, water-soaked or discoloured spots (yellow, brown, or black) often surrounded by a yellow halo.
- Progression: Spots enlarge and coalesce (merge), creating large dead patches of tissue.
- Secondary Effects: Premature leaf drop (defoliation), stunted growth, and reduced fruit quality due to impaired photosynthesis.
Favourable Conditions for Spread
- Weather: Thrives in high humidity (>95%), warm temperatures (20–30°C), and prolonged leaf wetness.
- Transmission: Pathogens spread rapidly via wind-blown spores, splashing rain, contaminated irrigation water, and dirty garden tools.
- Overwintering: Many fungi survive the winter on fallen leaf debris, re-infecting new growth in the spring.
Prevention and Management
- Sanitation: Rake up and burn fallen leaves to remove sources of infection.
- Watering Habits: Use drip irrigation at the base of plants; avoid overhead sprinklers that wet the foliage.
- Spacing: Ensure adequate space between plants to improve air circulation and reduce humidity.
- Chemical Control: Use fungicides like Hexaconazole or copper-based sprays, but only as a preventive or in severe cases.
- Natural Remedies: Spraying a 5% Neem leaf extract or neem oil has shown effectiveness in containing early infections.
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