Blight is a serious disease of potatoes and tomatoes, which can completely destroy the crop or make it inedible. Outdoor tomatoes are the most badly affected, blight is not as common on greenhouse tomatoes.
Blight causes discolouration of the leaves, turning them brown from the edges inwards. The leaves can dry and curl, although in moist conditions a white fungal growth can occur around the edges. The stems of the plants will also turn brown and in advanced cases the plant will collapse and die.
The fungus will also affect potato tubers and tomato fruit. Tomatoes will develop brown patches, can shrink and rot (even after picking). Potatoes will develop brown patches, which will eventually turn into slimy, smelly, rotten sores. Affected potato tubers and tomato fruit become inedible and have to be removed.
Carefully remove and destroy all affected parts as soon as you see them.
A degree of protection can be achieved by preventative spraying with a suitable fungicide. Spray before symptoms occur early in the growing season or in warm, moist conditions. Select a fungicide spray based on copper oxychloride. The same sprays can be used to treat any blight infected plants.
The occurrence of blight is very much dependent on specific weather conditions – when the right combination of warm temperatures and high humidity levels occur, blight will be prevalent.
As a result, it is possible to predict when blight will occur. There is a free service for farmers, which is available to gardeners, that will tell you when to expect it. Simply type in your email address and postcode and you will receive a Blightwatch Alert email when blight is in your area.