Sooty mold is frequently noticed on leaves of evergreen shrubs such as camellia, rhododendron, and laurel. In addition, Douglas-fir and other conifers are commonly affected.
Sooty mold is a black sooty fungus coating that develops on leaves and twigs. Cool, moist, cloudy weather of late winter and early spring hastens the mold growth. Several fungi (molds) grow in the sugary honeydew left on the plants by aphids, scale insects, pear psylla, white fly, mealybugs, and other insects that suck sap from the plant. Honeydew may drop on low shrubs from larger shrubs and overhanging limbs of trees. Sooty molds do not attack plants directly, but they can mar the beauty of the plant, and if extremely heavy, may shade out some light, causing the plant to be less vigorous. Sooty mold also will grow in honeydew on walls, fences, automobiles, or wherever it is present.
Sooty mold covers the leaf surfaces.
Control is achieved indirectly by controlling the insects that produce the honeydew on which the molds grow. Before an appropriate control strategy is undertaken it will first be necessary to identify what insect is causing the problem. If you choose an insecticide for control, before you purchase or use it be sure the plant or plants you want to spray are listed on the label. Then carefully follow label directions and precautions. Sprays may need to be applied periodically, from February through July, depending on the insects being controlled.
Once established, sooty mold is not easily removed, but sometimes part of it can be washed off leaves with strong streams of water from the garden hose. The mold gradually disappears after the insects have been controlled.
By
Ralph S. Byther, Extension Plant Pathologist, WSU Puyallup.
College of Agriculture and Home Economics, Pullman, Washington
Issued by Washington State University Cooperative Extension and the U.S. Department of Agriculture in furtherance of the Acts of May 8 and June 30, 1914. Cooperative Extension programs and policies are consistent with federal and state laws and regulations on nondiscrimination regarding race, color, gender, national origin, religion, age, disability, and sexual orientation. Evidence of noncompliance may be reported through your local Cooperative Extension office. Trade names have been used to simplify information; no endorsement is intended. Subject code 356. A.
EB1051
