Potato question - what am I doing wrong?

This is my second year as a plot holder and I seem to be having repeat problems with spuds.  They start of great, lots of healthy growth and foliage, but by this time in the year they seem to just die down and fall over.  Everyone else's plants on the site look all neat and healthy. 

Attached is a picture of one of my beds. This problem has affected all three potato beds of different varieties. I've had a dig and there are lots of ice spuds, but dont reckon they will get much bigger with the state of the leaves.  The only thing I can think is that I dont water the plants as much as I do other stuff, so could this be the issue?

Looks like blackleg.