Scab is caused by a bacterium. It is characterized by small, brown lesions on the tuber skin, seen at harvest. Scab development is enhanced by dry conditions and soils high in organic matter or recently amended with manure. Scab does not affect tuber quality, only appearance. Rotate the location of potatoes in the Garden to reduce the incidence of scab.
Early blight is characterized by small, target-shaped lesions on the foliage.
Lesions begin on lower, mature leaves. It is caused by a fungus. Proper soil moisture and fertility levels can prevent or minimize its incidence, because stressed plants are more susceptible. A fungicide treatment every 14 days will help control this disease. Early blight tuber decay rarely occurs in home Gardens if tubers are harvested gently, vines are completely dead prior to harvest, and skins are adequately set.