preventing black fly

Hi all you knowledgable folk

I have a cherry tree that has a severe infestation with black fly  I am not keen on chemical deterrents but would like advice on how I can limit these critters next year. I have tried the agri soap and garlic solution and put down jam for the ants but they are still there breeding away quite happily.......

by the way it is a new garden with a fairly heavy clay based soil so companion planting is always an option

Suggestions eagerly awaited

Thanx in advance