Potato Scab
Disease · Commonly affects: Potatoes, Jerusalem artichokes, Radishes, Turnips, Beetroot, Carrots
Potato scab, usually called common scab, is a soil-borne bacterial disease that marks potato skins with rough corky lesions. It is common on light, dry or alkaline soils in UK gardens and allotments. Although scabby potatoes are normally safe to eat after peeling, severe cases reduce their appearance, storage quality and usefulness as exhibition crops.
How to identify it
Check tubers at lifting time for rough, brown or tan corky patches. Lesions may be shallow, raised or pitted, and are commonly 2-15 mm across before joining into larger irregular areas. The affected tissue is dry rather than slimy, with no soft collapse or strong smell. Symptoms are confined mainly to the skin, though deep pitting can extend into the flesh. The foliage usually looks healthy, so the problem may not be noticed until harvest.
Damage
Common scab mainly damages the appearance and marketable quality of tubers. Shallow marks can be peeled away, but deeply pitted skins waste more potato and may make tubers dry out or admit other rots in store. Crops are seldom killed, yet heavily affected potatoes are disappointing for baking, showing and long-term storage.
Prevention
Grow varieties described as having resistance to common scab, and use sound certified seed potatoes. Avoid liming a bed intended for potatoes and do not add fresh wood ash, as scab is favoured by alkaline conditions. Keep soil evenly moist from the start of tuber formation until tubers have grown well, especially in dry weather. Use a varied rotation, avoid planting potatoes after heavily affected crops and add well-rotted organic matter to improve moisture retention.
How to manage it
Lift potatoes carefully once mature and sort them straight away. Use lightly affected tubers first, and discard any that are deeply pitted, split or developing secondary rot. Do not save heavily scabbed potatoes as seed. Record which beds and varieties were affected, then move potatoes to another part of the plot for several years. Improve the problem bed with organic matter and regular watering in future potato seasons, rather than trying to treat the harvested crop.
Potato Scab: frequently asked questions
How do I identify potato scab?
Check tubers at lifting time for rough, brown or tan corky patches.
How do I prevent potato scab?
Grow varieties described as having resistance to common scab, and use sound certified seed potatoes.
How do I get rid of potato scab?
Lift potatoes carefully once mature and sort them straight away.
General guidance for UK home gardens and allotments, focused on prevention and non-chemical control. For a confirmed diagnosis, the RHS or a local garden centre can help. Page updated 19 Sep 2026.