Question
Dear Jim,
I live in Belgium with a heavy soil garden.

My camelia bush is about 5 years old but has never looked very healthy. - yellowing leaves etc.
I have fed it bit it still has some yellowing leaves.
Originally I grew it in a pot but it seemed to need more space and now is in a sheltered border.

The major problem with it, is that most of the leaves are coated with a heavy brittle black surface.This can be scratched off with the fingernail but is not the answer to removing it permanently. I do not seem to have this on any of the other plants around.It is on the surface more than the underside

I have noticed a lot of ants crawling around the leaves - could they have anything to do with it?
Please can you help boost the poor plant.

It has actiually flowered quite well all things considered but generally it is in apretty unhappy ugly state

Thanks
Jane
can you please advise mesi  

Answer
The problem sounds like an aphid infestation rather then disease. Aphids are small insects that suck the juices out of plant leaves and excrete a substance called honeydew--a sugar liquid that a fungus called black sooty mold grows on. The leaves should feel sticky. This is what the ants are also after. Contol the aphids and the black sooty mold will be washed off by the rains. Check with your local garden/nursery type store and ask for a systemic insecticide that will control aphids. Spray this on the under side as well as the upper side of all the foliage. Here is a web link to information on Black sooty mold:
http://ohioline.osu.edu/hyg-fact/3000/3046.html