There is no question in my mind that your neighbor tried to be too nice and over fertilized. This is absolutely typical of a nitrogen overload. Potatoes should have a balanced diet of nutrients (N,P,K). Too much of any one will lead to one problem or another. I broadcast 10-10-10 before tilling (in addition to compost) and do not feed for the rest of the year. This works for me. Good luck!(posted 9649 days ago)Brad