Sooty mold

Sooty mold is a collective term for different Ascomycete fungi, which includes many genera, commonly Cladosporium and Alternaria. It grows on plants and their fruit, but also environmental objects, like fences, garden furniture, stones, even cars. The mold benefits from either a sugary exudate produced by the plant or fruit, or if the plant is infested by honeydew-secreting insects or sap suckers.

Sooty mold itself does little if any harm to the plant. Treatment is indicated, when the mold is combined with insect infestation.

Sooty mold is a collective, self-descriptive term for a number of different fungi; it is a black, powdery coating adhering to plants and their fruit or environmental objects.

The ecology of the different species, their interactions, relationship to the host have been little understood. A chance observation of a Microcyclospora tardicrescens inhibiting the growth of the fruit pathogen Colletotrichum fioriniae in dual culture tests, yielded trichothecolone acetate and its (S)-7-hydroxy derivative as active principles for the interaction between M. tardicrescens and C. fioriniae.

Genera causing sooty molds are Alternaria, Cladosporium, Aureobasidium, Antennariella, Limacinula, Scorias, and Capnodium.

Sooty mold grows particularly well on plants that produce a sugary exudate, if they are infested by honeydew secreting insects such as aphids, scales and the whitefly, or when infested by insects that suck sap from the host plant.

Sooty mold is commonly seen on the leaves of ornamental plants such as azaleas, gardenias, camellias, crepe myrtles, and laurels. 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. Occasionally citrus may exude sweet sticky secretions and sooty molds can grow on these.

...
Wikipedia