This disease, caused by a bacterialike organism, affects potatoes all over North America. Brown, corky areas or pits cover the outside of the tubers. Neutral and alkaline soils encourage the development of scab. Other susceptible crops include beets, turnips, carrots, rutabagas, and parsnips, although scab is usually not a serious problem on these.
Plant resistant potato varieties. Keep the soil pH below 5.2. Use a 3-year rotation between susceptible crops. Use well-composted manure in the potato patch; fresh manure may carry scab-causing organisms.
Photo courtesy of Sandra Jensen, Cornell University, Bugwood.org