Powdery scab – Spongospora subterranea

Symptoms   Small, slightly raised pimples under the skin which develop into round scab lesions about 5mm across.  Lesions erupt to release a fine powder of spores.  Affected eyes may produce tumour-like growths (cankers).

 Sources and Factors Favouring Development                       Seed and/or soil-borne; can be introduced to ‘clean’ land by dung from cattle fed on infected potatoes.

                        Favoured by frequent wetting/drying cycles following tuber initiation of susceptible varieties.

 Controls      Resistant cultivars are recommended however few cultivars have high levels of resistance to Spongospora subterranea. Avoid infected seed and visually free seed graded out of an infected crop.  Rest infected land for several rotations.  Do not feed infected potatoes to stock.  The most effective soil treatment at present for the control of Powdery scab is zinc oxide, but the benefits of applying zinc over the years has proved variable.