Dried tissue later falls out, leaving a pit or pox mark. Use clean, disease-free seed. Superficial brown irregular discoloration on the root. Under storage, the potato may deteriorate more rapidly because of moisture loss. See Black rot.
Plants become yellow and lower leaves drop off.
Base of stem becomes dark. When split open, a brown or black layer is found under bark. Use a three to four year crop rotation. Use resistant varieties. Consult seed catalogs for information on resistant varieties.