Camellias are broadleaved, flowering evergreen shrubs native to Japan and China. According to the Royal Horticulture Society, they are one of the most popular winter- and spring-flowering shrubs. Camellias are susceptible to attacks from a variety of insects and also to insect-related diseases such as sooty mould.
Insects such as aphids, scale, whiteflies and leafhoppers feed on plant sap. They exude a sticky-sweet watery substance called honeydew that falls on fruits and foliage. The sooty mould fungus grows on the honeydew.
The sooty mould fungus creates a thick covering of velvety-black fungal growth on the leaves, stems, fruit or any part of the plant where insects excreted honeydew. Sooty mould does not kill camellia plants, but heavy layers of fungal growth can interfere with photosynthesis, stunt plant growth and decrease plant vigour, leaving camellias susceptible to disease and insect attacks.
Sooty mould is usually more of an aesthetic problem than a threat to plant health. You control it by reducing or eliminating insect populations using horticultural oils, insecticidal soaps or chemical sprays. You can dislodge aphids from plants using a steady stream of water. Sooty mould does not penetrate the camellia plant's surface, so you can wipe or wash it from the foliage.