Powdery Scab Potato Disease

Powdery scab (Spongospora subterranea) is a fungal potato disease that affects tubers.  Due to the detrimental effects that powdery scab has on the tubers, it can often lead to the potatoes being rejected.

Common Signs and Symptoms of Powdery Scab

Symptoms of powdery scab include small lesions (abnormal tissue) in the early stages which develop into raised pustules which contain a mass of powdery spores.  These spore filled pustules often erupt, laving a rough and ragged, circular ring shaped scab.

Deforming cankers can develop on the tubers, and tumours often form on the plant’s roots.

Common Causes and Conditions of Powdery Scab

Powdery scab is caused by the fungus Spongospora subterranea and is widespread in many potato growing countries.  Powdery scab is spread by spores, normally from using diseased soil or via manure from livestock fed with diseased tubers.  The spores can survive in soil for many years, normally favouring heavy soils and cool, damp conditions.

Immune / Vulnerable Varieties

Potato varieties which tend to be more susceptible to powdery scab include Cara, Estima, Maris Bard and Maris Peer.  Kind Edward is particularly vulnerable.

There are a few varieties that have a good resistance to the disease, namely Sante and Hermes.

Controlling Powdery Scab

Cultural and Methods:
Powdery scab can be controlled by employing a good, long crop rotation and avoiding diseased seed.  Also, ensure that infected tubers are not fed to livestock.

There are currently no chemicals available in the UK to control powdery scab.