Sooty Mold
Disease · Commonly affects: Citrus, Tomatoes, Cucumbers, Squash, Peppers, Roses
Sooty mold is a dark, powdery growth of several harmless fungi that colonize the sticky honeydew excreted by sap-feeding insects. It seldom kills a plant on its own, but a heavy coating blocks light and is a clear signal that a pest problem needs your attention.
How to identify it
Look for a black to dark brown film that resembles a dusting of soot or ash on the upper leaf surfaces, stems, and fruit. Because it grows on the surface rather than infecting the tissue, it usually wipes or rubs off with a damp cloth, leaving healthy green tissue underneath. You will almost always find sticky honeydew and the insects producing it, such as aphids, whiteflies, scale, or mealybugs, on the plant itself or on a plant hanging above it.
Damage
A thick sooty layer shades the leaf and reduces photosynthesis, which can slow growth and trim yields when coverage is severe. On fruit and foliage the harm is mostly cosmetic staining, and the mold's real importance is that it flags an underlying insect infestation that is the true source of plant stress.
Prevention
Keep plants vigorous with good spacing and airflow, and avoid overfeeding with nitrogen, which pushes soft new growth that aphids and other honeydew producers favor. Scout regularly for sap-feeding insects, since stopping the honeydew is what prevents the mold, and control ants that tend and protect those insects. Where possible, avoid siting susceptible plants directly beneath trees or shrubs that drip honeydew from above.
How to manage it
Because the fungus lives on honeydew, aim your effort at the insects producing it: knock aphids and whiteflies off with a strong spray of water, prune out heavily coated or infested shoots, and gently wash or wipe the film from leaves and fruit you want to keep clean. Encourage natural enemies such as lady beetles, lacewings, and parasitic wasps, and use sticky bands or other barriers to keep ants from farming the pests. Once the honeydew supply is cut off, the existing sooty mold dries, flakes, and weathers away on its own.
General guidance for US home gardens, focused on prevention and non-chemical control. For a confirmed diagnosis and options specific to your area, contact your local Cooperative Extension office. Page updated Aug 4, 2026.