Deux-Sèvres, France

I have a mega problem -a virus ? Leaf curl/black fly/Lilly beetle with my cherry trees this year. The leaves are being eaten by something and there is a black substance coming from them which is having an effect on the plants underneath. My question is: as it is probably too late but also impossible to deal with the source (cherry trees too high) what or how should I help the plants underneath?
There are various different ones from annuals to perennials and established shrubs.

• 28 Jun, 2012