See:
Camellia - Sooty Mold (Black Mold)
Note: These are saprophytic fungi that live on the excrement of insect pests. Dark, brown-black, powdery fungal growth occurs over leaf surfaces. Severe black fungal growth will almost completely cover the upper leaf surface. Black fungal growth may cover anything that the excrement falls on including other plants and even the walls or windows of an adjacent house. Manage aphids that excrete honeydew.