"Tuber symptoms of common scab vary in ext … "Tuber symptoms of common scab vary in extent and appearance. Common scab lesions are usually circular and 0.25 to 0.33 inch (6 to 8 mm) in diameter, but they can be smaller in early stages of development and larger if they coalesce. Lesions typically possess a raised margin and slightly depressed center. Some characteristic symptoms have descriptive names: russet scab appears on tubers as superficial tan to brown corky lesions; pitted scab is characterized by lesions with depressions beneath the tuber surface; and raised scab appears as cushionlike, warty lesions. Common scab lesions can be confused with tuber lesions of powdery scab caused by Spongospora subterranea and patchy russetting caused by Rhizoctonia solani. In addition to tuber symptoms, Streptomyces spp. can cause brown stem and stolon lesions." can cause brown stem and stolon lesions."