Sooty mold is an unsightly dark brown or black coating on leaves and stems that can be removed by rubbing. It is the result of a fungus growing on honeydew excretions made by insects such as aphids, white flies and mealy bugs. Sooty mold usually causes little direct damage, but it can decrease the plant’s vigor by reducing photosynthesis in the leaves.
To control this problem, you must first take steps to decrease the insect population causing the problem. In most cases, aphids are responsible for sooty mold in home landscapes. Aphids can be effectively controlled with several insecticides. Before using an insecticide, make sure it is labeled for use on the plant you plan to spray and follow all the label’s instructions. If you need help choosing an insecticide, call the Extension Office at 638-2548 for more detailed information. Or if you had rather not use an insecticide, you can get satisfactory results using an insecticidal soap to control this pest.
But, controlling the insects will not remove the black coating; it will only prevent it from getting worse. Although it is not necessary, sooty mold can be washed from the leaves by drenching them with detergent (mixed at four ounces per gallon of water), waiting three to four minutes and then washing with a strong stream of water.
If you have sooty mold and are not sure what insect is causing the problems, bring some of them by the Walker County Extension Office at 102 E. Napier Street in LaFayette to get them identified and find out what will best control them.
Norman Edwards is coordinator of Walker County Extension Service.