The leaves of camellia are covered with a black layer. What has caused this? Scale insects excrete a sticky substance, called honeydew on the leaves. Sooty mould then develops on the surface of the honeydew.
Although sooty mould looks unsightly, it will not kill the plant.
Sooty mould on camellia
How to get rid of sooty mould on camellias
Control. Look out for scale insects and white egg masses on the underside of the leaves in early spring and summer. Remove the insects with a damp cloth.
Wipe off the sooty mould with a damp cloth or sponge and water. Add a few drops of dish soap to the water.