Disease on Plum Tree

My Plum Tree seems to have some sort of disease, towards the end of July, there seemed to be a lot of flies and wasps on the leaves, now all the leaves have little holes in them, the fruit have slits on them and there are flies and wasps eating them. Overall the tree looks unhealthy with the leaves wilting now.Also the beech hedge seem to be full of little white flies, and some leaves looked very black and dead now. What can I do.