Late blight — how to recognize and can you save your tomatoes

Late blight — quick diagnosis and action

Phytophthora infestans is a fungus that can destroy an entire tomato bed in 2–3 weeks during wet summers. It was the cause of the great famine in Ireland in the 19th century. In the garden, it's an equally serious threat.

How to recognize:

• Brown spots with greenish edges on leaves — starting on lower leaves
• In humid weather: white fluffy coating ON THE UNDERSIDE of spots
• Browning and rotting of stems
• Fruits with hard brown spots that rapidly expand

  Conditions favoring blight:

• Temperatures 15–25°C
• Humidity above 90% for at least several hours
• Wet leaves

  What to do when you notice first symptoms:

  1. Immediately remove diseased leaves (to trash, not compost)
  2. Spray with copper-based fungicide (Miedzian, Cuproflow) — stops spread
  3. Improve ventilation — remove leaves near ground so air circulates
  4. Stop watering leaves completely

     Prevention:

  5. Plant in windy and sunny locations — dry leaves provide protection
  6. Growing under cover/polytunnel
  7. Resistant varieties e.g. Phantasia, Primabella
  8. Preventive spraying with copper fungicide every 10–14 days in wet years

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