Crape Myrtle Sooty Mold and Aphids: Causes and How to Fix It
A black, sooty film over the leaves — often with a sticky feel underneath — is a common and unsightly crape myrtle problem. The mold itself is a symptom: something is feeding on the tree and dripping sugary honeydew. Here are the likely causes, ranked, with how to tell them apart and what to do about each.
Crape myrtle aphids (the usual culprit)
What's happening
Tiny pale-green or yellowish aphids cluster on the undersides of leaves and suck sap, excreting sticky honeydew that coats everything below them. A black fungus called sooty mold then grows on that sugary film, blackening leaves, branches, and anything beneath the tree. The aphids weaken the tree and the mold blocks light from the leaves, but the mold itself doesn't infect the plant.
How to confirm
Turn over a few leaves: clusters of small soft-bodied insects mean aphids. Leaves, lower branches, and the ground, deck, or car beneath the tree feel sticky from honeydew, and a sootlike black coating develops on top of that — it rubs off, unlike a true leaf disease. You may also notice ants farming the aphids for their honeydew.
How to fix it
Knock light infestations off with a strong jet of water, then treat the undersides of leaves with insecticidal soap or neem oil, repeating every week or two until the aphids are gone — controlling the insect stops the honeydew and the mold dries up and weathers away on its own. Encourage ladybugs and lacewings, which devour aphids. The black film can be rinsed off over time once feeding stops.
Prevent it
Inspect leaf undersides through summer and treat aphids early, keep the tree vigorous but not over-fertilized (lush nitrogen growth attracts aphids), and protect beneficial predators by spot-treating rather than broad-spraying.
Crapemyrtle bark scale
What's happening
A relatively newer pest, this white, felt-covered scale attaches to the bark of trunks and branches rather than the leaves. Like aphids, it sucks sap and excretes copious honeydew, often producing even heavier sooty mold and dramatically blackened trunks. Crushed scales bleed pink, a useful identifying trait.
How to confirm
Look at the bark, not just the leaves: small white or gray waxy bumps encrusting the trunk, branches, and pruning knuckles, which ooze pink when squashed. The trunk and limbs turn strikingly black with sooty mold, often worse than aphids alone cause, and the encrustations stay put when you try to brush them off.
How to fix it
Scrub the trunk and reachable branches with a soft brush and mild soapy water to dislodge scale and remove mold, then apply horticultural oil to smother overwintering scale, thoroughly coating the bark. Severe infestations may warrant a systemic insecticide applied per label and timing; consult local guidance, as treatment windows matter. Persistence over a season or two is usually needed.
Prevent it
Inspect the bark each year for the first white specks and treat early before it spreads, avoid moving infested plants, and keep trees healthy so they tolerate the pest better.
Honeydew dripping from a plant above
What's happening
Sometimes the crape myrtle is innocent and the sticky honeydew is raining down from an aphid- or scale-infested tree growing overhead, with sooty mold then colonizing the crape myrtle's leaves below. The pest is on the neighbor, not your tree.
How to confirm
You find sooty mold and stickiness on the crape myrtle but no aphids on its leaves or scale on its bark, while a larger tree directly above it is clearly infested. The mold is heaviest on the upper, exposed leaves that catch the drip from above.
How to fix it
Treat the source plant overhead for its aphids or scale rather than the crape myrtle, since stopping the honeydew at its origin is the only lasting fix. Rinse the crape myrtle's foliage to remove existing mold; it will clear once the drip stops.
Prevent it
Keep overhanging trees and shrubs free of sap-sucking pests, or site crape myrtle out from directly beneath them.
When to worry (and when not to)
A little sticky residue and light sooty film is mostly a cosmetic nuisance and won't kill a healthy tree. Worry when the black coating covers most of the canopy and shades out the leaves, when honeydew is constant and heavy, or when you find white pink-bleeding scale encrusting the bark — a building infestation that saps vigor and bloom over time. Knock down the insect causing it and the sooty mold takes care of itself, and the tree bounces back.