Eaten foliage

Shothole.
It is called this as it looks like the leaves have been shot with a shotgun. It is a strength sapping disease known as bacterial canker.
It also occurs in Beetroot, Horseradish, Plums, Peaches and Cherries.
Cherries seem to have it's most severe form and weeping wounds can develop.
The disease is very hard to eradicate but it can be controlled in fruit trees by spraying them three times at three-week intervals with a copper compound, starting in August after fruit harvest.
A spray when the petals fall is also advisable, although it can cause damage in certain varieties of tree.

This is from a readers digest book "Your garden questions answered"

It also mentions that the cause could be soggy ground. Try improving the drainage nearby.

I hope this helps.

If canker as Trees suggests then nasty - there is die back to each affected branch and dead leaves remain on tree.For any chance of saving cut out affected areas well back to new growth and seal cuts with tree paint .Spray tree with Bordeaux mixture.All removed should be burnt and any tools used for pruning sawing should not be used on anything esp other healthy trees shrubs etc as highly contagious.Good luck.