Infestation on my Red Robin

Hi.

I recently planted a new hedge consisting of young Photinia plants.  I noticed lots of damaged leaves and on further investigation lots of (I think) aphids (black and green), being tended to by some black ants.  They are quickly destroying the new leaves as they appear.

Can anyone advise me on the best (most effective) way to get rid of these?

Many thanks.

Chris.