black leaves on apple tree

I have three apple trees in my garden, Last year two of them had fruit, but the third trees leaves were nearly all black, we treated them with bug killer and cut off all the effected leaves when we pruned the tree.

This year two of the trees have blossom on but the third, whilst showing good signs of healthy leaves, they have started to turn black. and the tree has no blossom nor any sign of any.

Can any one shed light as to what the problem might be and the best way to resolve it. the three trees are similarly aspected.

Petermac