Welcome back Jcee! No, nothing you could do to prevent aphid infestation, other than spraying with a systemic insecticide prior to going away. Not a great idea on fruiting trees, only certain ones can be used on those, best to treat when the problem arrives.

Just as I thought, lets hope the plum tree recovers. The cherry plum seems to be ok now and beginning to show new leaves so maybe my Victoria plum will do the same!!

I find that greenfly hate antibacterial fairy liquid with eucalyptus (diluted!). But of course with the rain we've had lately it would just wash it straight off anyway.

I've read that companion planting against aphids works by using garlic bulbs next to plant that is troubled by them. It works for me with roses, I don't know if it would work for your tree but may be worth a try. Good luck.

Thank you Fuchsia fan and Juliernorth-never thought about companion plants,though bit akward with my trees!
That's exactly what my wife said,use diluted fairy liquid!!
Thank you both.