This disease occurs as wart-like growths on the foliage and fruit of infected plants. On the tubers of potato plants, the scab can appear as either indented or raised areas of growth. Keep the pH level low. Too much alkalinity will only encourage the growth of scab. For organic gardeners this means not to use wood ashes where scab has been a problem.
Sulfur is said to be an effective control also.
Use ammonium sulfate or sulfur to increase acidity of the media or soil. Wet media and spray with elder leaves. Can also be controlled by drying out growing area, reducing humidity.