Quick Facts
- Black or dark gray coating on bark, leaves, and twigs
- Sticky residue on surfaces below trees
- Reduced light penetration to foliage
- Cosmetic discoloration
What Is Sooty Mold?
Sooty mold is a dark, soot-like fungal growth that develops on leaves, twigs, and branches wherever a sticky, sugary residue called honeydew has settled. The fungi responsible (commonly Capnodium, Scorias spongiosa, and Fumago vagans) do not infect the tree itself; instead, they live on honeydew excreted by sap-feeding insects, or, less often, on sap leaking from bark wounds.
How to Recognize It
- A black, gray, or charcoal-colored coating on leaves, twigs, and bark that can look painted on or dusted with soot.
- A thin, papery film that may peel or flake off as it dries.
- Sticky leaves, or a sticky, shiny residue on cars, patios, sidewalks, or understory plants beneath the tree.
- Presence of aphids, scales, whiteflies, mealybugs, or psyllids on the tree above (the insects producing the honeydew).
- Reduced leaf color and, in heavy cases, slowed growth, premature leaf drop, or dieback because the coating blocks sunlight needed for photosynthesis.
- Ants or wasps actively visiting the foliage, attracted to the honeydew.
Sooty mold tends to appear and worsen during the warm growing season, when sap-feeding insect populations peak and produce the most honeydew. In Atlanta, heavy build-up is often most noticeable from June through September.
Why It Matters for Atlanta Trees
Sooty mold itself is mostly a cosmetic issue and does not infect tree tissue, but when the coating is heavy or persistent it blocks sunlight, which can reduce photosynthesis and lead to slowed growth, leaf loss, dieback, and in extreme cases death of the affected plant. Just as importantly, sooty mold is a signal that a sap-feeding insect infestation is active on or above the tree, and that underlying pest problem is what needs early attention. In Atlanta, it is most often noticed on crape myrtle, tuliptree (yellow poplar), southern magnolia, maple (especially sugar and red maple), hackberry, oak, pine, beech, holly (including Nellie Stevens), gardenia, azalea, and camellia.
Why this needs an ISA-certified arborist
Sooty mold is a symptom, not the underlying problem, and the real cause can be any of several different insects (soft scales, armored scales that do not produce honeydew but look similar, aphids, whiteflies, mealybugs, psyllids) or even bark wounds, each calling for a different response and timing. An ISA-certified arborist can identify which pest is responsible, assess how much canopy and structural impact has occurred, and recommend a safe, tree-appropriate plan, especially on tall trees where inspection and any treatment require trained climbers or specialized equipment.
Suspect sooty mold on your tree? Schedule a free on-site visit from EastLake's ISA-certified arborists at request a free estimate or call 404-850-1174.
General Prevention
- Keep trees vigorous with proper watering during Atlanta droughts and a 2 to 4 inch ring of mulch (kept off the trunk) so stress does not invite pest outbreaks.
- Inspect susceptible trees and shrubs (crape myrtle, magnolia, holly, maple, tuliptree) regularly for the sucking insects that produce honeydew, and look up at any larger tree growing above plants that have turned black.
- Avoid over-fertilizing with high-nitrogen products, which encourages soft new growth that aphids and other sap-feeders prefer.
- Prune to maintain good airflow and light penetration through the canopy, and avoid wounding bark with mowers or string trimmers, since sap from wounds can also feed sooty mold.
What NOT to Do
- Do not self-diagnose. Many tree problems look alike, and treating the wrong one wastes time and can harm the tree.
- Do not apply fungicides, insecticides, or other chemicals without an arborist's specific recommendation. Wrong product or wrong timing makes things worse.
- Do not assume that scrubbing or power-washing the mold off will solve the problem. The fungus will return as long as the honeydew-producing insects (or sap-leaking wounds) above the affected surface go unaddressed.
Related Services
For most diagnosis and treatment questions, the right starting point is one of our services:
- ISA-Certified Arborist Services for diagnosis, consultation, and second opinion.
- Plant Health Care (PHC) for ongoing tree health management.
- TRAQ Tree Risk Assessment when the tree may be a safety hazard.
Sources
This page summarizes general information from: University of Georgia Extension (Bartow County), NC State Extension, and Clemson Cooperative Extension Home & Garden Information Center.