Potato blight, also called late blight, is a destructive fungal disease that is caused by spores of Phytophthora infestans. Potato blight spores are spread on the wind and may also contaminate potato tubers in the soil. It can ruin a crop in 10-14 days and there is little that can be done to save an infected crop. It was the original cause of the Irish Potato Famine.

How to Recognise Blight on Potatoes

• If you want to be a blight buster be aware that it is particularly prevalent during warm humid weather. It can be especially problematic in summer from June onward during wet weather.
• Dark brown blotches appear on the leaves, particularly towards the leaf tips and edges. White fungal spores develop around these lesions on the undersides of the leaves, and further lesions develop on the stems.
• Leaves and stems rapidly blacken and rot causing plant collapse.

Prevention of Potato Blight

• Always plant healthy disease free seed potatoes from a reputable supplier.
• Choose blight resistant potato varieties such as the Hungarian Sarpo range developed specifically for their superb resistance to late blight and other viruses.
• Blight resistant varieties allow the gardener to produce reliable disease free crops without the need for constant spraying.
• Always choose an open planting site with good airflow and leave sufficient space between plants. Better airflow will allow the foliage to dry quickly after rainfalls and therefore slows the spread of blight between plants.
• Crop rotation will help to prevent a build up of disease, and will avoid infected plants springing up undetected from potato tubers that were missed during last year’s harvest.
• Spray potato crops with a protective fungicide such as Dithane 945 before signs of blight become apparent.

Blight Resistant Potatoes

• Maincrop Potato varieties Kifli, Blue Danube, Shona, Verity and Cara a pinkish red-eyed tuber.
• First Early Potato varieties Orla and Lady Balfour
• Potato ‘Sarpo Mira’ – Huge yields of tasty, floury tubers. A real all-rounder for all cooking purposes.
• Potato ‘Sarpo Axona‘ – Sister line to the phenomenally popular Sarpo ‘Mira’. The tubers are more regular in shape and the flesh is slightly more creamy. Superb flavour for all culinary uses.
• Potato Valor an oval white skinned tuber with eelworm and blight resistance.

Cultivation for Blight Buster Potatoes

• If plants become infected they should be removed and destroyed not added to the compost heap.
• Where potato crops have already developed tubers then these can be saved by cutting away the foliage and stems. Leave the soil undisturbed for 2/3 weeks to kill off any lingering spores so that they don’t infect the crop when it is lifted.
• Given that old potato tubers can harbour blight spores over winter, it is important to destroy any unwanted or diseased tubers.
• Spores may also be washed into the ground by heavy rainfall to infect tubers growing there causing a red-brown rot directly beneath the skin which slowly spreads towards the centre of the tuber.
• The spores are released on the wind and quickly spread to infect neighbouring plants.

Credits
Potatoes by Buzz Hoffman CC BY-NC-SA 2.0