Sooty Mold

Taxonomy

Domain

Scientific Name

Common Name

sooty mold (general)

Compiled by Ned Tisserat, Colorado State University:

Sooty Mold
Various genera and species of fungi

Hosts

All species of trees that are hosts to large populations of certain insects in the order homoptera which produce a liquid secretion called honeydew on which sooty mold fungi grow.

Diagnosis and Damage

Sooty molds vary in appearance from thin dark patches to irregular, blackish masses covering large areas. They may be found on any of the above ground surfaces of host plant such as trunks, leaves and upper surfaces of branches. Although widespread and conspicuous, these groups of fungi cause little damage to plants other than affecting, to a limited degree, the function of affected leaves. They can be a nuisance if growing on honeydew deposited on automobiles, outdoor furniture... anything that is under an aphid or scale infested tree.

Biology and Disease Cycle

Sooty molds are entirely superficial saprophytic fungi that derive nourishment from insect and plant secretions. These fungi reproduce by ascospores, conidia, and sometimes by fragmentation of hyphae. The most common nutritional substrate for these fungi is honeydew, a liquid secretion released from the anus of aphids, soft scales, mealybugs, and some species of leafhoppers. Honeydews are complex mixtures of sugars, amino acids, proteins, other organic substances, and minerals. Droplets of honeydew often fall from insect-infested leaves or branches and stick to other plant parts or to objects such as automobiles, sidewalks, or outdoor furniture. Both honeydew and spores of sooty mold fungi are dispersed in water during rain. Thus dark fungal deposits often occur on plant parts and on other surfaces not infested by insects.

Conditions Favoring and Management of Disease

Plants vulnerable to high population of insects known to produce honeydew often exhibit a layer of sooty mold. Infrequent, minimal amounts of rainfall allow honeydew to build up on plants creating perennial cases of sooty mold on many trees. Management options include controlling levels of honeydew producing insects on host plants, and spraying or washing down plants to remove honeydew. Both of these options are not particularly feasible for large trees nor for street trees.

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