Ornamentals and Turf Insect Note Logo

SOOTY MOLDS

Steven D. Frank & Stephen B. Bambara, Extension Entomologists and 
R. K. Jones, Extension Plant Pathologist (retired)

CAUTION: This note was developed for North Carolina and may not apply to other areas.


[General Information] [Biology] [Control] [Other Resources]

General Information

Sooty molds are really fungi that grow microscopic threads that become abundant enough to form easily visible black spots. When very abundant, sooty molds cause plants to appear dark and sooty or almost uniformly charcoal gray. Occasionally, sooty molds form a continuous thin sheet that eventually peels away from the plant surface like delicate black tissue paper. Microscopic examination reveals the sooty mold threads may be matted down or more or less cemented together. Capnodium sooty molds have various kinds of spore forming structures.

Biology

sooty mold on leaf

Sooty molds occur in all parts of North America. Capnodium citri is associated with whiteflies and scale pests on citrus. Capnodium elongatum is associated with scale pests of tuliptree, oleander, osmanthus and other ornamental plants. Other species of Capnodium are associated with insect pests of fig, crape myrtle, azaleas and many other plants. Scorias spongiosa is associated with aphid and scale pests of alder, pine, beech and other trees. Fumago vagans is associated with sucking pests of linden and other trees, shrubs and even house plants. Sooty molds are not plant parasites. They develop in honeydew, a sweet, sticky liquid excreted by aphids, scales and other sucking insect pests that feed from the phloem tissue. However, sooty molds lessen the aesthetic value of ornamental plants, and lower the vigor of plants by blocking sunlight essential for photosynthesis. The combination of feeding by a large number of aphids or scales and the heavy coating of sooty molds may drastically reduce the vigor and beauty of ornamental plants.

sooty mold on azaleaSooty molds are associated with sucking insect pests (aphids, scales, mealybugs, psyllids) that extract sap from the phloem tissue. Soon after a plant is heavily infested with such a pest, it is usually covered with honeydew. Sucking pests ingest copious amounts of sap to extract nutrients. Much of the water and sugars in the sap pass though the insect are excreted. Unless washed off by rain, the honeydew clings to the plant (and objects below). Spores or fragments of sooty molds are blown are carried to the honeydew and new colonies of sooty mold develop. Although the fungal threads may adhere tightly to the plant surface, sooty molds do not parasitize plant tissue. Instead, they develop exclusively on honeydew. However, even after the source of honeydew is eliminated, sooty molds may adhere to plants and other objects for months afterward.

Control

The first step in control of sooty molds is to suppress the aphids, scales or other pests that are excreting the honeydew on which sooty molds subsist. If one of the horticultural oils is used for control, it also has the advantage of helping to loosen sooty molds frorm the plant surface. This hastens the weathering away of the sooty molds. Horticultural oils are formulated by many companies are available through garden centers, hardware stores, and like establishments. The rates of application vary with time of year. If horticultural oils are applied to tender, new growth, damage to the plant may occur. Growing season rates may be lesser than dormant season rates.

Numerous other insecticides are labeled for aphids, scales, mealybugs and other sucking insects. These insects are covered in more detail in some of the other insect notes. When using any pesticide, be sure to follow the directions for safe use found on the label.

Useful Links:
How to recognize sooty molds USDA
UC Davis IPM


Other Resources

For assistance with a specific problem, contact your local North Carolina Cooperative Extension Service personnel.

Published by North Carolina Cooperative Extension Service

Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
Originally prepared by: James R. Baker and Stephen B. Bambara, Extension Entomologists and R. K. Jones, Extension Plant Pathologist (retired)

ENT/ort-41 March 1997 (Revised November 2002)

Web page last reviewed January, 2011 by the webperson