Black mildew and sooty mold are often used interchangeably though sooty mold should be used for the black mold that grows on insect excrement (honeydew) that can coat the leaves, stems, and/or fruit of plants. The mold is not parasitic but can reduce the leaf’s photosynthetic ability by blocking out light. It is a common indication that the plant is infested with piercing-sucking insects, such as aphids, scale, mealybugs, or whiteflies. Sooty mold can be removed by washing it off with warm soapy water. Controlling the insects that are causing the honeydew is required for long-term control.

Black mildew is a true plant parasite that can resemble powdery mildew in appearance only black rather than whitish. Black mildew is a minor problem in the lower Midwest but a species can cause witches' brooms on serviceberry. Black mildew can cause more serious damage in the Deep South.