Symptoms

• Symptoms on foliage

Under disease pressure, the symptoms appear sporadically, and mainly in hot summers.
The typical symptom is premature death of the haulms with drying of the foliage extending from the top to the bottom of the plant: the leaves turn yellow and curl upwards (photo 1). These symptoms are similar to those of Verticillium wilt.

At the end of the growing season, the base of the stems and the underground parts of the plant display signs of typical infection: early destruction of the roots, detachment of the root envelope and numerous black dots on the base of the stem (microsclerotia) (photo 2).

• Symptoms on tubers

Lesions on tubers caused by fungal infection can be observed (photos 3 and 4): irregular and diffuse light to dark greyish surface areas with or without the formation of fructifications (microsclerotia) with setae when tubers are exposed to moisture (photos 5 and 6). Fructifications due to black dot (microsclerotia) are larger than for silver scurf (conidiophores) (photo 7).

When tubers have been subjected to cold temperatures, development of deep sunken lesions are sometimes associated with dry rot of the underlying tissues (photo 8).