Blight

Blight is a fungal infection – Phytophthora infestans – which affects plants in the solanae family, most often potatoes and tomatoes but I have found it also on chilli peppers.

The spores land on wet foliage and will spread rapidly when temperatures are above 10 degrees C and humidity is over 25% for two days or more.

Symptoms

• Dark brown patches on leaves and stems sometimes surrounded by a pale yellow halo
• Fruits and tubers start to rot, tomatoes turn brown

Reduce the Risk

• Keep an eye out for “volunteer” potato and tomato plants from last year and dig up and compost straight away
• Use good quality seed potatoes from a reputable source, discard any that look unhealthy
• Grow potatoes in at least a four year rotation
• Grow plants with wide spacing between for good air circulation. Avoid growing tomatoes and potatoes next to each other as they can pass on the infection
• Grow tomatoes under cover.
• Avoid getting the leaves wet and watering in the evening as the disease likes wet and warm conditions to develop.
• Earth up potatoes to avoid passing the infection on to the tubers – provide extra cover with grass clippings or straw
• Remove any infected foliage as soon as you spot the disease. A dry spell can halt the spread of the disease and you may not lose all your crop if you spot it early.
• Grow blight resistant varieties

  What to do with infected foliage, tubers and fruit

• Remove any infected foliage and compost in a covered hot heap or take to council green waste bin – the fungus will not survive in dead plant material
• Harvest tubers at least three weeks after the removal of infected foliage
• Infected tubers and fruit can be buried deep in the ground (2 foot) or taken to council green waste
• Don’t save seed from infected tomatoes as the disease can survive through the winter in the seed
• Garden Organic does not recommend the use of copper based sprays (Bordeaux Mix) as these are only effective as a preventative measure on healthy foliage
• Eat or cook any fruit from infected plants as soon as possible