Q What is black scurf?
A A fungal disease (Rhizoctonia solani) which damages early potato shoots in cold, wet soils. Later, it infects and damages stems and tubers, which develop black spots.

Caption: Black scurf may look unattractive but the potatoes can still be eaten

Q How do I recognise black scurf?
A Look out for black speckles, which can be scraped off the tubers. Earlier in the season, watch out for brown stem bases; these infected areas may go right around the stem. The leaves become rolled and wilted. A white powdery collar can sometimes be seen around the stem at ground level, too. In severe cases, where they are planted in cold soils, the young sprouts are killed and the crop does not survive.

Q Could I mistake black scurf for anything else?
A You could mistake this for the more serious blackleg disease, but the stems in this disease are blackened at ground level and the plants killed. Leaf-roll virus also affects the foliage.

Q When should I expect black scurf?
A It is carried on the seed, or is already present in the soil. It is most likely to occur when the conditions are cool and on light soils.

Q What can I do about black scurf?
A The spots don't look good, but the potato beneath is sound and can be cooked as usual. Losses are from extra peeling, not reduced yield. Sprout potato seed indoors and delay sowing until the soil is warm; mid-April should be fine. As an extra insurance, a fleece covering will warm the crop up. Try not to grow potatoes on the same spot of ground more often than once in three years.