Silver scurf (Helminthosporium solani) is a ubiquitous fungal blemish disease of potatoes. It is first visible as small silvery grey spots that enlarge into circles, which may show a slightly darker margin.

Black dot (Colletotrichum coccodes) is a common superficial fungal blemish on potatoes. The black dots are microsclerotia that are often just visible to the naked eye. They can be found on tubers, stolons, roots and stems.

Common scab (Streptomyces scabies) is an unsightly disease of potatoes that has very little affect on storability. The blemish is caused by a bacteria-like organism called an actinomycete. Lesions may be circular or angular and may coalesce into large irregular areas.

Powdery scab (Spongospora subterranea) is a fungal blemish disease of potatoes, which first shows as small raised pimples beneath the skin. As they develop, the skin breaks open to expose a dark brown powdery mass of cystosori or spore balls.

Black scurf (Rhizoctonia solani) is an entirely superficial black fungal incrustation on the tuber surface. It usually appears as small, irregular blemishes that are, in fact, compacted masses of mycelium called sclerotia.

Skin spot (Polyscytalum pustulans) is generally an invisible fungus until after approximately 2 months of storage, when the infected tissue begins to show spots. They tend to be bluish black and slightly raised.