Sooty Mold (fungi – Capnodium spp., Fumago spp., and others): Sooty mold is a name commonly given to a condition that is not truly a disease, but a black coating on leaves, branches and fruit made up of fungal growth. The fungus is usually dark colored and powdery-like, hence the name sooty mold. The fungi associated with this condition are saprophytic, that is, they do not feed on live plant tissue, but rather thrive on insect secretions with a high content of sugars. These secretions, known as honeydew, are particularly common with aphids, scales, white flies, and other insects. The insect honeydew provides nourishment for the fungus, and under proper conditions, the entire plant may be covered with the sooty mold.
A black velvety coating made up of the fungal strands is formed on the surface of leaves, twigs and fruit. If the honeydew is light, it may appear only in spots. As a general rule, the black fungus coating usually can be rubbed off easily from the surface of leaves, fruit or branches. With time, the fungus may dry-off, become flaky, and fall off. If for some reason the insect infestation decreases, the amount of sooty mold also will decrease. If no insects are present to cause a re-infestation, rains will usually wash off most of the sooty mold. The fungi causing sooty mold are known to occur on citrus, oleander, gardenia, fig, crapemyrtle, azaleas, pittosporum and many other ornamental bushes and trees. Control can be obtained by applying insecticides that reduce insect populations. Using oil formulations as insecticides is effective, since oil gets rid of many of the insect pests and also softens the black fungus so it can be washed off easier by rain or other means.