Powdery and Common scab are both potato blemish diseases that cause unsightly scab-like lesions on the tubers which may in turn result in the tubers being rejected or downgraded.

The symptoms are restricted to the underground parts of the plants.

This can cause significant financial implications for growers. Effective and timely identification of these diseases is critical as a result.

Common scab caused by the bacteria Streptomyces scabiei, a common soil-borne pathogen, is prevalent across a range of potato varieties.

Powdery scab is caused by Spongospora subterranea which can also vector the Potato mop top virus, a source of spraing.

This test uses a microscopic visual examination to give an indication of the most likely cause of the scabs. Molecular testing can then be offered as a confirmatory method.

If there are multiple scabs, the test will be performed on the predominant symptom unless instructed otherwise.

When sending plant pathogens and invertebrate samples from outside England and Wales for testing please email the Crop health team (crophealth@fera.co.uk) who will issue you with the relevant Letter of Authority to ensure your samples are not delayed upon entry to the UK.