Silver scurf fungus only attacks tubers. Symptoms usually appear first at the tuber stem end as small, circular or irregular silver and gold blemishes or lesions. Field soils may be a source of spores when potatoes are grown consecutively, without crop rotation.
Lesions may expand and cover most of the tuber surface. The skin may also thicken, creating a rind. The silvery appearance is more noticeable when the tubers are wet. Tuber lesions that develop in storage are circular and dark brown to black. They increase in size and coalesce, rendering the tubers unmarketable. In storage, infected tubers lose water through the lesions, so some shriveling and wrinkling may occur.
The blemishes that develop on the tuber surface lower the value of the crop and water loss from infected tubers leads to shrinkage and economic loss. Silver scurf has also been associated with decreased seed tuber vigour.
Lesions may be difficult to detect at harvest, especially if the tubers are not washed. Tubers that appear to be disease free may develop symptoms in storage. Most economic damage usually occurs after tubers have been stored for three months or more, however, smooth-skin cultivars suffering severe infection at the time of harvest can be unmarketable.
