get rid of white aphids on my plum tree

[grimaldi]

My plum tree (Italian prune) has white aphids all over the leaves at the ends of the branch (on the new growth). I sprayed them with an insecticidal soap and it killed them but I don't want to spend $10 for a bottle that only lasts for 2 complete sprayings. Anyone know of a home-made or less expensive way to kill these white aphids?

[opabinia51]

A jet of water is usually sufficient to knock them off the tree. Perhaps a weekly spraying of neem oil might help as well. Read up on Neem oil in the General Forum first though.

[TLL]

I also have green aphids taking over my young plum tree, and bought some neem oil (made by Grotek) the other day. After reading the instructions on the bottle for mixing with water, and spraying the tree, only a couple of hours later it seemed that the aphids were gone (except for the few clinging to life at the end of the branches). Now its two days later, and they are back with a vengence! The instructions on the bottle said 2 tsp of oil per litre of water - should I up my concentration and try again? Any other suggestions? I had sprayed the area around the base of the tree as well, but they are all over that as well...

Help!?!?!?
TLL