Potato wart disease attacks all parts of the potato plant except the roots. It infects meristematic tissues with easily recognizable symptoms. The tumors are initially composed of parenchymal tissue, and subsequently, the growths resemble cauliflower with a diameter of 1–8 cm. Often the tumor covers the entire tuber, or there are only large tumors without distinct tubers. Above the surface, they are green to brown. Towards the end of the growing season, they turn black and disintegrate. Below the surface, tumors appear at the base of the root collar, stolons, and around the eyes of the tubers. They are whitish to brown and may not be noticed until harvest. Tumors can also develop during storage. During this period, the symptoms of wart disease may be confused with what is known as pseudowart. This refers to the spontaneous sprouting of all buds in the tuber eye.
