Cherry tree sickness

Can someone advise on what might be wrong with my cherry tree, and how I can go about treating it? The leaves are shrivelling and turning black. It's affecting the entire tree badly. It usually looks healthy in summer (apart from one year where ants were farming on it and damaging the leaves, but I stopped that with a sticky band round the tree trunk).

I've tried Googling for answers, but it seems like it could be one of many things.