Circular Spot and
Sclerotial Blight (fungus - Sclerotium rolfsii): Although caused by
the same organism these two diseases are completely different. Sclerotial blight
is a seed bed disease. The white, coarse fungus grows wildly on bedded roots,
causing sprouted slips to die. It is easily identified by sclerotia that develop
in the fungal growth [Image]. Sclerotia are balled
up strands of the fungus, about the size of mustard seed, that serve a survival
function. They are white at first but progress to a dark brown color. No fungal
structures are observed with circular spot which is a very common problem on storage
roots. Lesions are round and up to one inch in diameter. As potatoes dry in storage,
the skin in the center of the spot may crack. Circular spots seldom progress in
size in storage. There is no chemical control available. Crop rotation is advised.
Early harvest may reduce incidence since infection seems greater later in the
growing season.
