Park under a hackberry in Melissa in late summer and you learn this fast. The hood gets sticky. The windshield smears. Half the leaves carry a black film, as if the tree stood downwind of a fire. Nothing burned. The tree has a bug problem, and the black film is just the symptom.
What honeydew actually is
Leaves make sugar, and sap carries it. Aphids, soft scale, psyllids, and whiteflies tap into that flow and drink more sugar water than they can use. The extra passes through and drops. That drop is honeydew. It lands on the leaves below, on the lawn, on the car, on anything parked or placed under the canopy. It is clear and sticky at first. Within days it turns dark as mold moves in.
Each local tree has its usual culprit. Hackberries get the woolly hackberry aphid, a tiny white insect that can coat a whole street in August. Crape myrtles get aphids on the new tips and, far worse, bark scale on the trunks. Pecans drip from aphids in midsummer. Live oaks and red oaks host scale and aphids in the crown, the same drip our oak weeping sap guide sorts from wetwood and spring bleed. If the trunk itself is weeping dark fluid, that is a different problem. Honeydew falls from the leaves. It does not run out of the bark.
Sooty mold: ugly, shallow, and honest about the cause
Sooty mold is a group of dark fungi that live on honeydew. The fungus does not infect the leaf. It grows on the coating, the way mold grows on a jar lid. Rub a black leaf and the film smears off to show green underneath. That rub test tells you more than any photo ID app.
The harm is indirect. A thin coating costs the tree almost nothing. A heavy coating, leaf over leaf for a full season, cuts the light the leaf can use, so the tree makes less food heading into fall. Seedlings, shrubs, and turf under the drip suffer more than the tree does. The mold also holds the real message: something is feeding up top, in numbers, and it has been feeding for weeks. Killing the mold without stopping the insects is wasted work. Our bark scale guide makes the same point about crape myrtles. Wash the black off and it returns in a month if the scale is still there.
Find the insect before you treat anything
Stand under the tree on a calm morning and look at the undersides of the leaves. Aphids cluster there and along soft new shoots. They are small, soft, and often green, black, or white and woolly. Scale looks different. It sits still on twigs and bark, like a bump or a crust that is part of the tree until you scrape it and it comes off as a separate shell. Check for ants. Ants protect aphids from predators and move them to fresh growth, so heavy ant traffic up the trunk often means aphids in the crown.
Use our tree diagnosis guide if the tree shows more than drip and black film. Yellowing with green veins points to iron chlorosis in our alkaline clay. Dieback at the tips, bark coming off in sheets, or mushrooms at the base point somewhere else entirely. Honeydew alone, on an otherwise full and green crown, is a nuisance problem. Honeydew plus thinning and dead wood is a stressed tree asking for a fuller look.
The fix, in the order that works
Blast it with water. A strong jet from a hose, aimed at the leaf undersides, knocks most aphids off. They do not climb back well. Repeat every few days for two weeks on a small tree. On a large shade tree this step is partial, but it costs nothing and it cleans the car and patio today.
Cut back the worst of it. Aphids pile onto soft, overfed growth. Skip heavy nitrogen fertilizer on a tree that already drips, and prune out infested tips and crowded interior shoots. Better air flow dries leaves faster. Our trimming and pruning page covers cuts that open a crown without lion tailing it.
Protect the predators. Ladybugs, lacewing larvae, and tiny parasitic wasps eat aphids by the hundreds. A broad spray kills them too, and aphids rebound faster than predators do. That rebound is why a sprayed tree often drips worse in July than in May. Spot treat the worst branches if you spray at all.
Use oil or a systemic only when the case earns it. Dormant oil in late winter smothers overwintering scale and eggs on crape myrtles and fruit trees. A soil applied systemic can clear a bad woolly aphid year on a hackberry over a patio, the case our hackberry guide walks through. Both are for heavy, repeat cases, not a light coating on a full crown.
Keep the tree strong and the drip stays small
Stressed trees get hammered first. A hackberry or oak that rides out August on no water, in compacted clay, carries more aphids and recovers slower. Deep water in a long dry spell, using the method in our drought watering guide, and a wide mulch ring kept off the flare do more for next year than any spray. Healthy trees still get aphids. They feed fewer of them, and predators catch up sooner.
The short version: sticky means insects, black means mold on their waste, and the mold is not the disease. Find the feeder, blast it with water, prune for air, and save chemicals for repeat cases.
Common Questions
What is the sticky stuff falling from my tree?
It is honeydew, the sugary waste that aphids, scale, psyllids, and whiteflies drop while they feed on leaf sap. It coats leaves, cars, and patio furniture under the canopy. Ants farm aphids for it, so ants up the trunk are an early clue. On a hackberry, the usual culprit is the woolly hackberry aphid. On a crape myrtle, check the bark for scale first.
Will sooty mold kill my tree?
Almost never by itself. Sooty mold is a black fungus that grows on honeydew, not inside the tree. It blocks sunlight and slows growth on a heavily coated tree, and it looks bad. The insects doing the feeding are the real problem. A young, stressed, or heavily infested tree loses vigor over a season or two. A healthy mature oak usually rides out a light year with no lasting harm.
How do I get rid of honeydew and sooty mold?
Start with water. A hard hose blast knocks aphids off leaves and washes honeydew off hard surfaces. Prune out the worst infested tips and open the crown so air moves. For scale, scrub the bark and use dormant oil in late winter. Skip broad sprays that kill ladybugs and lacewings, since those predators do most of the work for free. Once the insects stop, new growth comes in clean and rain wears the old mold off.
When should I actually treat instead of leaving it alone?
Treat when the drip ruins a driveway, patio, or pool deck you use every day, when a young tree is coated and stalling, or when the same tree gets hammered two years in a row. Leave it alone when the coating is light, the tree is mature, and predators are already working. A soil applied systemic is an option for bad hackberry and crape myrtle cases. Read the label and keep it off flowering plants that bees visit.