Scot Nelson, CC license via Flickr. Gardenias are prized for their very fragrant white flowers and glossy, dark green leaves (Figure 1). https://gardenerspath.com/how-to/disease-and-pests/sooty-mold The name is pretty descriptive. The sooty substance is actually called sooty mold, and it is a fungus that is spread by insects. Good air circulation (about 10 cm minimum of clearance) around all sides of the plants helped too. What Was the Black Soot on My Gardenias? Sooty Mold: White flies indirectly cause infestation of sooty molds by leaving a honeydew-like substance wherever they feed on the gardenia plants. It doesn’t attack plants directly. If you control the aphids, you will also be able to control sooty mold. Be sure to check your plants frequently and deal with any gardenia pests quickly to reduce the damage they cause. Sooty Mold Velvet-textured black mold disfiguring you gardenias follows infestations of sap-sucking insects, including aphids, soft scales, mealybugs and whiteflies. However, this method of prevention is time-consuming. The black stuff on the leaves is a fungus called sooty mold. Although sooty mold doesn't penetrate the plant tissues, it can weaken it by blocking sunlight. Control sooty mold on plants by stopping it before it starts. These molds then feed on this honeydew substance, making a black film over the foliage and stem. Sooty mold is commonly seen on the leaves of ornamental plants such as azaleas, gardenias, camellias, crepe myrtles, Mangifera and laurels. That’s the case with sooty mold. Understanding how a problem starts can save time and effort in trying to control it. The fungi causing sooty mold are known to occur on citrus, oleander, gardenia, fig, crapemyrtle, azaleas, pittosporum and many other ornamental bushes and trees. It takes around 2-3 weeks for black, sooty mold to appear after infestation by insects. This fact sheet provides a brief look at this popular plant. Karuka is affected by sooty mold caused by Meliola juttingii. “The leaves are black. I tried rubbing the black off, but the black remains. ... Black Sooty Mold. Sooty mold is a black, smut-like substance that grows in the sugary secretion of sucking insects such as aphids, scales, mealybugs, and whiteflies. “My poor gardenias are suffering!” writes faithful reader, Sheri Chamblee. Sooty mold thrives on the honeydew created by gardenia bugs like aphids. If you have gardenias or crape myrtles, you’ve probably seen it. Make sure they are receiving full sun, especially if close to an irrigation head. Control can be obtained by applying insecticides that reduce insect populations. The most successful method of preventing mold on a gardenia plant is early intervention. 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