green fly

Can anyone tell me what to get for green fly on my acer tree?

 

A jet from a hosepipe will dislodge them if it's a large tree,a soap water spray will will kill them.

 

Thanks walnut I shall try the jet from a hose pipe.

 

A longer term plan would be to grow a few nettles (in a bucket) as the smell apparently attracts ladybirds, provide good nesting sites for ladybirds, lacewings and hoverflies, and grow plenty of nectar rich flowers in an attempt to get hoverflies to move in.