Plant Disease

High Severity

Late Blight

Affects: Tomato, Potato · Monsoon and post-monsoon (high humidity + mild temperature 15–25°C)

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Causal Organism

Phytophthora infestans (water mould / oomycete)

Symptoms

Water-soaked lesions on leaves that turn dark brown with white fungal growth on the underside. Fruits develop brown, greasy patches. In humid conditions, the entire plant can collapse within days.

Prevention

Use resistant varieties (Arka Rakshak for tomato). Avoid overhead irrigation. Ensure good air circulation by proper spacing. Remove and destroy infected plant material immediately.

Season Risk: Monsoon and post-monsoon (high humidity + mild temperature 15–25°C)

Treatment

Apply mancozeb (0.25%) or metalaxyl-mancozeb (0.25%) at first sign of disease. In severe outbreaks, use systemic fungicides like cymoxanil+mancozeb. Spray every 7–10 days during humid weather.

Frequently Asked Questions

How fast does late blight spread?
In humid conditions (above 85% RH) and temperatures of 15–22°C, late blight can destroy an entire field within 7–10 days if not controlled. Act immediately at the first sign.
Can I eat affected tomatoes or potatoes?
No. Infected fruits have mycotoxins and poor taste. Discard infected produce and don't use infected potato tubers as seed.

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