[Elm street]

When we took over our plot earlier this year it had an apple tree and a plum/gage tree already on it.
The apple tree looks to be doing fine and has a good crop of fruit on it, the plum/gage? Has a decent crop but is absolutely covered in aphids & greenfly, to the extent that if you stand under the tree it feels like it is raining due to the honeydew dropping from them.
Both of the trees are overgrown and need to be pruned this year, is there anything I can do to fight off the pests in the meantime?

Thanks for any response!
Mel