This section is from the book "Commercial Gardening Vol4", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
This is caused by Oospora scabies, a fungus that usually attacks the young tubers, forming scattered roughish patches or scabs on the surface, sometimes spreading all over. To prevent this disease from spreading, only healthy unscabbed tubers should be planted, and the ground should be deeply dug and allowed to sweeten by exposure to the atmosphere before planting. If too much stable manure has been used, lime should be added to rectify it; or if too much lime has been used (as is sometimes the case), then well-rotted stable manure may be dug in the previous autumn or early in spring.