Scab-like lesions on potatoes, beets, carrots and other root crops is a common problem worldwide. Fortunately, it is an aesthetic problem and does not affect the plant’s productivity or flavor and best of all they are safe to eat.
Reduce the risk of scab causing diseases with proper selection and care. Grow scab resistant potato varieties like Norland, Norgold Russet, and Superior when possible. And always use certified disease free seed potatoes.
Add organic matter to the soil to increase drainage, and reduce compaction. Grow potatoes in slightly acid soil whenever possible.
Rotate plantings. Some research has found planting potatoes in areas where broccoli and other brassicas were grown the previous season appeared to reduce the incidence of scab.
Water properly and do a thorough clean up in fall.
A bit more information: You will see less scabby potatoes in soils with a pH of 5.2 or lower. Lime is added to raise the soil pH while sulfur is used to lower pH. Altering the soil pH is challenging and when done improperly can have a negative impact on your garden. Always have your soil tested before attempting to change the soil pH.