Plum tree covered in aphids - save it or cut it down?

I have a plum tree about seven years old at my dacha near Tula, and this season it's just been covered in black aphids. The leaves are curling, young shoots are drying out. I tried spraying it with soapy water - didn't help much. Maybe this is already too far gone and it would be easier to just remove the tree than try to save it?