Sooty mold

Sooty molds are Ascomycete fungi which grow on plant exudates and the sugary honeydew secreted by insects such as aphids, scales, the whitefly, and other insects which suck sap from their host plants.

Plants located under pecan or hickory trees are particularly susceptible to sooty mold, because honeydew-secreting insects often inhabit these trees. The honeydew can rain down on neighboring and understory plants. The fungus itself does little harm to the plant; it merely blocks sunlight, and very rarely may stunt a plant's growth and yellow its foliage.