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Late Blight in Tomato

How to identify and treat late blight in Tomato.

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Tomato care requirements

water
Deeply and regularly; 2–5cm per week. Consistent moisture prevents blossom end rot.
soil
Rich, well-draining soil with good organic matter. pH 6.0–6.8.
light
Full sun — 8+ hours daily.
symptoms

Symptoms to look for in Tomato

Large, water-soaked, greyish-green blotches on leaves that quickly turn brown and papery, often with white fungal growth visible on the underside in humid weather, and can affect stems and fruit.

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Common causes in Tomato

Caused by the water mould Phytophthora infestans, which spreads rapidly in cool, wet weather and can destroy a tomato crop within days if unchecked — historically the cause of the Irish potato famine on the related potato plant.

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How to treat late blight in Tomato

Remove and destroy all affected plant material immediately (do not compost), and apply a copper-based fungicide preventively if late blight is active in your area. Severely affected plants should be removed entirely.

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Preventing late blight in Tomato

Avoid overhead watering, ensure good airflow, and choose blight-resistant tomato varieties in areas where late blight is common.