Help me save my potatoes!

I didnt get to watering them one day, they got kinda droopy and its been downhill from there. The leaves and stalks perked back up a bit but they never did return to their full upright nature. Soon I started noticing yellowing and spotted leaves. I sprayed with a fungicide, and they are well fertilized but that doesn't seem to have helped. Someone please help me save these, they were doing so well.

 

This is a duplicate Loofah, original post discussed here:

http://gardenerscorner.co.uk/forum/threads/whats-happening-to-my-potatoes.52085/

(I think too early / cold for Main Season Blight though ...)

 

Over watering? if you water daily...

 

I water my container-grown spuds several times a day, once the plants get to a decent size. Its hard to keep the compost most at all in fact.

 

It's a mixture of potting soil and store bought compost. I water it maybe 1 once a week, it stays moist pretty well, theyre in a half wine barrel.