Sooty mold is a black, flaky growth on plant leaves, stems, and trunks that is often confused for some sort of plant disease. In-stead of being the cause of a plant problem, it is a sign that insects have been feeding—specifically, those of the “piercing-sucking” variety named so because of their specialized mouthparts like tiny needles that extract plant sap.

What goes in must come out! The sugary excrement of these insects is a perfect substrate for growth of the black, sooty mold. Other insects in this category also associated with sooty mold are aphids, scale insects and mealybugs.

After insects are treated, sooty mold will remain on plant leaves until it eventually washes off. Spraying with soapy water and using a strong hose stream to rinse is one way to remove sooty mold. Fungicides are not effective or necessary.