I had the same problem last year but just in my tomatoes. They were planted in the same spot my potatoes are this year. This year both have "it". It's just the new growth at the apical ends that curl from the sides and the end. It has been wet and hot but I'm in sand and it's well drained. I've treated with maneb and sevin. Tomatoes are mainly better boy and all potatoes are yukon gold. Do have photos but they're too big for this post. Could send via email if it would be any help.