Aphids, Honeydew, and Sooty Mold: Why Your Rochester Tree Drips Sticky Sap and Turns Black
By Linda Marsh, Pests & Diseases. Last updated: June 25, 2026
That mysterious sticky coating on your windshield, patio furniture, or driveway under a maple or linden is one of the questions Rochester homeowners ask most each summer. The good news: the sticky sap and the black film are the same problem, and it is treatable once you understand what is feeding it.
Why is my tree dripping sticky sap onto my car?
The "sap" is not sap at all. It is honeydew, a sugary liquid excreted by sap-feeding insects living in the canopy above. Aphids, soft scale, the invasive spotted lanternfly, and a handful of other insects pierce the tree's vascular tissue (the phloem) and drink the sugar-rich sap. Because they take in far more sugar than they need, they excrete the excess as a fine, sticky mist that rains down on everything below.
In Rochester, the usual suspects are aphids on maples, lindens, and oaks, plus soft scale insects. If the stickiness is heaviest in late spring and early summer and you can find tiny pear-shaped insects clustered on the undersides of new leaves, aphids are the likely cause. If you instead see waxy bumps stuck to twigs and leaf veins, you are probably dealing with soft scale, which we cover in depth in our guide to soft scale on magnolia, maple, and oak.
What are aphids and why do they show up here?
Aphids are small, soft-bodied insects, usually green, black, yellow, or reddish, that reproduce explosively in warm weather. A single aphid can give birth to live young without mating, so a light infestation can become a heavy one in a matter of weeks. Our Zone 5b-6a climate, with warm humid stretches between lake-effect weather systems, gives several generations a chance to build up over a single growing season.
They tend to target tender new growth, which is why heavily fertilized or recently pruned trees sometimes flush with soft tissue that aphids love. Maples are a classic host in our region, and aphid complaints on Rochester maples spike every June. Lindens take a beating too: the linden (basswood) aphid is a familiar nuisance on street and yard trees around Monroe County.
Want a certified arborist to take a look?
Monster Tree Service of Rochester offers free estimates and a full plant health care program across the Rochester area.
Get a Free Estimate →What is the black film on my tree leaves and surfaces?
The black, sooty coating on leaves, bark, sidewalks, and car hoods is sooty mold, a group of fungi that grow on the honeydew, not on the plant itself. This is the single most important thing to understand: sooty mold is a symptom, not the disease. The fungus is feeding on the sugar coating left by the insects. It does not infect or feed on living tree tissue the way apple scab or anthracnose does.
A heavy layer of sooty mold is not harmless, though. Cornell's IPM resources note that a thick coating can block enough light to reduce photosynthesis, which stresses an already-burdened tree. So while the mold itself will not kill your tree, the insect population producing the honeydew is the real problem that needs attention.
Why are there so many ants on my tree?
If you notice a steady stream of ants marching up and down the trunk, they are not the cause of the sticky sap. They are a clue. Ants farm aphids and soft scale the way humans keep dairy cows: they protect the insects from predators (like ladybugs and lacewings) in exchange for the honeydew. A busy ant highway on the bark is one of the most reliable signs that you have a honeydew-producing insect colony in the canopy above.
Break the chain at the insect and the rest unravels. The dripping stops, the ants move on, and new growth and rain clear the old sooty mold over time.
Should I wash off the sooty mold or spray a fungicide?
Neither is the real fix. Because sooty mold is only growing on honeydew, a fungicide is the wrong tool: there is no leaf disease to kill, and the mold will simply return as long as the insects keep feeding. Washing leaves or hard surfaces removes the cosmetic black film temporarily, but new honeydew will recoat them within days.
The durable solution is to control the insects producing the honeydew. For a light, accessible aphid outbreak on a small shrub or low branch, a strong jet of water or an insecticidal soap can knock populations down, and encouraging beneficial predators helps. But for a full-sized shade tree dripping onto your driveway, spraying the canopy is impractical and often ineffective.
Want a certified arborist to take a look?
Monster Tree Service of Rochester offers free estimates and a full plant health care program across the Rochester area.
Get a Free Estimate →When does systemic soil treatment beat spraying?
For mature trees, the most effective approach is usually a systemic treatment applied to the soil or trunk. The tree takes the material up through its roots and moves it into the leaves and phloem, exactly where the sap-feeding insects are drinking. This reaches the entire canopy without blanketing the neighborhood in spray, and it tends to last through the season.
Timing and dosage matter, and product selection depends on the tree species, the specific insect, and proximity to pollinators and water. This is genuinely a job for a credentialed professional rather than an over-the-counter guess. If you are not sure whether what you are seeing warrants a treatment plan, our piece on when to call an arborist for tree insects walks through the decision. And if the sticky sap is one of several symptoms, our broader guide on why your tree looks sick helps you sort cause from effect.
FAQ
Will sooty mold kill my tree? Sooty mold itself does not infect or feed on living tree tissue, so it will not directly kill a healthy tree. A heavy coating can block sunlight and reduce photosynthesis, which adds stress, and the underlying insect infestation is the real concern.
Do I need to wash the black film off my leaves? You do not have to for the tree's sake, and washing only helps temporarily. Once the insects are controlled and the honeydew stops, new growth and rain will gradually clear the existing sooty mold on their own.
Are the ants on my tree damaging it? The ants are not feeding on the tree. They are tending aphids or scale for honeydew, so their presence is a useful diagnostic sign rather than a separate pest problem to treat.
Is the sticky sap dangerous to my car's paint? Honeydew and sooty mold are mostly a sticky, unsightly nuisance, but letting them bake onto paint or glass for long periods can make cleanup harder. Move parked cars out from under an infested tree until the insects are managed.
Can I just spray something from the hardware store? For a small shrub or a low, reachable branch, insecticidal soap or a strong water spray can help. For a full-sized shade tree, over-the-counter sprays rarely reach the whole canopy effectively, which is why a systemic treatment from a certified arborist is usually the better route. Schedule an arborist evaluation with Monster Tree Service if you are unsure.