sticky bay tree remedy

I have a little bay tree in a pot and its covered in sticky residue and its turning the leaves black.
There are some lavae or similar on the underside of the leaves and i understand this is the problem.
What is the best way to treat it?
Is there a way to prevent it in the future?
thanks

 

Can you provide us with some pictures please Aidan?

 

I had that happen here. I laborously wiped each leaf down with water, a squirt of washing up liquid with a splash of hydrogen peroxide after I had removed very bad leaves. Spraying it occasionally with such can help to keep things under control.

 

It's probably aphids on the underside of the leaves creating honeydew and black mould growing on the honeydew.
If you don't use the leaves for food purposes a spray with a general insecticide will sort out the aphids then give it a good spraying with diluted washing up liquid and before it dries give it a hard spraying with clear water.
It should then wash off the worst of the sootymould.