Sooty Mold
Sooty mold is a black, soot-like fungal film that grows on the sticky honeydew excreted by sap-sucking insects.
Sooty Mold at a glance
| Also known as | Sooty mould, black mold |
|---|---|
| Affected parts | Leaf and bark surfaces |
| Most at risk | Any tree with a sap-sucking pest (aphids, scale, whitefly, mealybugs) |
| Main cause | Mold growing on honeydew excreted by sap-sucking insects |
| Severity | Cosmetic, but blocks light; the real issue is the pest causing it |
| Reversible? | Yes — clears once the pest is controlled |
What to look for
- Leaves: A dull black, sooty coating on upper leaf surfaces that wipes/rubs off (the leaf is green underneath); a sticky, shiny honeydew layer; reduced vigor from shaded leaves.
- Whole tree: Ants on the trunk; the sap-sucking pest itself somewhere above the mold.
Overview
Sooty mold is a black, soot-like fungal film that grows on the sticky honeydew excreted by sap-sucking insects. It doesn't infect the plant directly, but it coats leaves and bark, blocking light and looking alarming. It is best understood as a symptom: where there is sooty mold, there is (or was) an aphid, scale, mealybug, or whitefly infestation — usually above the blackened area.
Causes
Honeydew from aphids, soft scale, mealybugs, or whitefly feeding above; warm, still conditions; ants farming the pests.
Commonly confused with
It is itself a clue, not a primary disease. Don't confuse the wipe-off black film with leaf-spot fungus (which is in the leaf) or with dark mildew. If it wipes off and there's honeydew/insects above, it's sooty mold.
Which species are affected
Any species hosting a honeydew-producing pest; common on citrus-relatives, ficus, camellia, crepe myrtle, and indoor trees.
Treatment
Treat the underlying pest (see Aphids, Scale, Mealybugs, Whitefly) — that stops new honeydew. Then wipe/wash off the mold with water and a little mild soap; horticultural oil both controls pests and loosens the film. Control ants. The mold won't return once the pest is gone.
Prevention
Keep sap-suckers in check (inspect, quarantine, treat early); control ants; maintain airflow; rinse dusty/honeydew-prone foliage.