Join the RHS today and support our charitable work
Keep track of your plants with reminders & care tips – all to help you grow successfully
RHS members get reduced ticket prices
RHS members get free access to RHS Gardens
Free entry to RHS members at selected times »
Reduced prices on RHS Garden courses and workshops
020 3176 5800
Mon – Fri | 9am – 5pm
Help us achieve our goals
Join the RHS today and support our charity
A number of fungi and bacteria are capable of causing decay in potato tubers. Symptoms are often present at lifting, but some of the problems will also spread through stored tubers, and a few will only develop after prolonged storage.
Black leg (Pectobacterium atrosepticum) on potato 'Charlotte'. Credit: RHS/Pathology.
Potato tuber rots are a frequent cause of losses prior to, or after, lifting. Significant problems often follow a wet growing season, particularly if the tubers are then lifted from wet soil. Some of the pathogens causing tuber rots also produce symptoms on the aerial parts of the plant.
You may see the following symptoms:
Blackleg develops when bacteria spread along the stolons from decaying stems and enter the daughter tubers. Contaminated seed tubers are the most important source of the blackleg bacterium (Pectobacterium atrosepticum). Both this and the soil-borne soft rot bacterium (P. carotovorum) can also infect tubers via damage, or act as secondary colonisers following other diseases. Wet soil during growth and lifting of the crop make bacterial problems much more likely.
Blight affects the tubers when spores are washed down into the soil from lesions on the foliage. Blight does not spread to any extent during storage, but secondary bacterial rots do, and can cause extensive losses. The fungus-like blight pathogen also affects tomato crops.
Pink rot, dry rot and gangrene are caused by soil-borne fungi. Any damage suffered by the tubers at lifting will make them much more prone to infection. It may take weeks or even months of storage for symptoms of dry rot or gangrene to develop.
In addition to those mentioned above, there are several other diseases causing decay of tubers, e.g. rubbery rot, violet root rot, watery wound rot. The bacterial diseases brown rot and ring rot, whilst unlikely to develop in garden crops, are caused by notifiable organisms. Where significant problems develop it may be worth having a sample examined by experts to determine the cause.
PotatoesPotato and tomato blightPotato blacklegPotato black scurf and stem cankerPotato scabsRoot vegetables: storing
the RHS today and get 12 months for the price of 9
RHS members can get exclusive individual advice from the RHS Gardening Advice team.
The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.