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Potato blight

Symptoms

The first signs appear in early summer as brown or black areas at the tips and margins of the leaves, which then curl and wither. It can spread quickly causing the plant to collapse. The spores can also spread from the leaves to the potatoes in the ground. Infected tubers have a firm reddish-brown rot under discoloured skin. They are usually invaded by a secondary fungus which makes them smell awful. Potato blight can also infect tomatoes, causing the fruit to rot on the plant.

Cause

It is caused by the fungus Phytophthora infestans. The spores are spread by wind and rain, especially when humidity is high and the air temperature is a minimum of 10oC (50oF). Infected tubers from the previous year can also reinfect crops.

Treatment

Infection of the tubers can be reduced by earthing up around the plant stem. Removing infected leaves immediately will also help save the crop. Plant blight resistant varieties, such as 'Romano'. Spray with Murphy Copper Fungicide as soon as symptoms first appear and then every two weeks. As a preventative measure you can also spray Murphy Copper Fungicide every two weeks from July.

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