Symptoms

• Symptoms on tubers

The symptoms of skin spot on tubers consist of small dark pustules, 0.5 to 4 mm in diameter, which develop on the surface of tubers, either isolated (photo 1), or grouped around the eyes or at the heel-end (photo 2). The lesions are prominent conical pustules which are usually surrounded by a depressed ring (photos 2 and 3). The underlying tissue is corky and detaches itself easily.

The symptoms can develop during the first weeks of storage if drying is insufficient.

• Symptoms on sprouts, roots and stolons

On growing crops, superficial brown and cracked lesions similar to those found with black scurf can develop on the roots and stolons. On emergence, sprouting tubers can be infected and the bud tips can be completely killed by the fungus, resulting in poor emergence or reduction of the number of stems.