Image placeholder
Potato scab
Streptomyces scabies
Bacterial diseaseLow impact
A soil-borne bacterial disease causing rough, corky patches on the skin of potato tubers. Purely cosmetic - tubers are safe to eat and flavour is unaffected - but affected skin may need to be peeled more generously.
Key facts
- Type
- Bacterial disease
- Affects
- Potato
- Active season
- May - Sep
- Peak season
- Jun - Jul
- Vulnerable stages
- Growing · Harvesting
- Spread rate
- slow
- If confirmed
- Monitor
Signs & symptoms
- -rough, corky, raised or pitted patches on the tuber skin
- -patches may be superficial or slightly sunken
- -plant foliage typically looks healthy
Management
Do now
- -Remove and store unaffected tubers promptly
- -Peel away scabbed skin before eating - flesh beneath is fine
Prevention
- -Keep soil pH around 5.5-6.0 - scab is much worse in alkaline soils; avoid liming potato beds
- -Rotate potatoes to fresh ground each year
- -Avoid adding fresh manure in the season before growing potatoes
- -Water consistently during tuber development (June-July) - drought stress significantly worsens scab
Further reading
- -Potato scab is caused by soil bacteria, not a fungus - it is favoured by dry, alkaline, sandy soils
- -Consistent watering during June and July (when tubers are swelling) is the single most effective preventive measure
- -Unlike most potato diseases, scab does not render tubers inedible