Written by The Executive Tree Care Team
You may already be dealing with spotted lanternfly damage. If you’ve been seeing more of them in your yard this month, you’re not imagining it. Adults are active right now across Delaware County, Montgomery County, and Chester County, all three remain under Pennsylvania’s Spotted Lanternfly Quarantine as of this month. And late summer isn’t just when they’re most visible. It’s the season right before they start laying eggs for next year, which makes right now the window where what you do actually matters.
Here are five signs your trees may already be dealing with lanternfly damage, and what’s usually behind them.
1. Sap Oozing or Weeping Wounds on the Trunk
Spotted lanternflies feed by piercing bark and pulling sap directly from the tree. On a tree with heavy feeding pressure, you’ll often see wet, weeping patches on the trunk where the insects have been feeding, sometimes with a fermented smell. This isn’t cosmetic. Repeated feeding wounds stress the tree and open it up to secondary problems.
2. A Black, Sooty Coating on Leaves, Furniture, or Pavement
As lanternflies feed, they excrete a sugary waste called honeydew. It coats everything underneath the tree, patio furniture, cars, decks, walkways, and it promotes the growth of black sooty mold on top of it. If you’ve noticed a sticky black film building up under a specific tree that wasn’t there last year, that’s usually your first real clue something is feeding heavily above.
Even attached properties aren’t immune. One of our team members dealt with this personally, a tree-of-heaven wasn’t even on their own property, it was next door. But the spotted lanternfly activity and the sooty mold that came with it didn’t stay put. With connected garages, the mess crossed right over onto a shared wall. You don’t need the host tree in your own yard to end up dealing with the consequences of one nearby.
3. Swarms of Adults on the Trunk, Especially at Dusk
By August, spotted lanternflies are in their adult stage, roughly an inch long with distinctive spotted wings. They tend to cluster low on tree trunks in large numbers, particularly in the evening. If you’re seeing dozens at once on one tree rather than a few scattered insects, that tree is likely a preferred feeding site, not just a passing-through spot.
4. Thinning Canopy or Dieback on an Already-Stressed Tree
A tree that’s already dealing with drought stress, storm damage, or root issues has fewer resources to spare when lanternflies start feeding on top of that. If you’re seeing branch dieback or a thinning canopy on a tree that’s also showing lanternfly activity, the two are often connected. Stressed trees draw more attention from pests generally, not just lanternflies.
5. A Tree-of-Heaven Growing On or Near Your Property
This is the one most homeowners miss entirely, because it doesn’t look like a threat. Tree-of-heaven (Ailanthus altissima) is spotted lanternfly’s preferred host tree in Pennsylvania. It’s a fast-growing, weedy tree that seeds itself aggressively along fence lines, property edges, and neglected corners of yards, and it’s frequently mistaken for sumac or just written off as brush. Once you know what to look for, a sapling is easy to spot and easy to remove while it’s small. Left alone, it becomes a magnet for exactly the kind of infestation described above, sooty mold on outdoor furniture and parked cars included.
A Real Job: Protecting Nine Host Trees in West Chester
Not every tree showing lanternfly activity is a candidate for removal, and not every host tree is the invasive kind. In 2021, the Executive Tree Care team treated nine host trees inside a fenced backyard in West Chester using bio-stimulant deep root injection inoculated with a systemic material to control spotted lanternfly through multiple instar stages, the different growth phases the insect passes through from nymph to adult.
Systemic treatment works differently than a surface spray. The tree takes up the material through its root system, and it stays effective as lanternflies feed across those different life stages, rather than protecting for only a few days after application. It also does double duty: the same root injection that controls active feeding also improves the tree’s overall health and vigor, supporting a tree that’s already under feeding stress rather than just targeting the pest and leaving the tree to recover on its own.
This is the option for valuable, established trees you want to keep, oaks, maples, and other landscape trees that are lanternfly hosts but aren’t the invasive species driving the infestation in the first place.
Why This Matters Right Now, Not in the Spring
Female spotted lanternflies begin laying egg masses in September and October, each one holding 30 to 50 eggs, on tree bark, fence posts, outdoor furniture, and almost any flat surface. One tree-of-heaven left standing through the fall can seed next year’s infestation for an entire block. Removing a tree-of-heaven now, before egg-laying starts, is one of the few actions a homeowner can take that actually reduces next year’s population rather than just reacting to this year’s.
When to Call a Professional
Small tree-of-heaven saplings can often be pulled by hand. But mature trees, especially ones close to structures, power lines, or property boundaries, need a professional removal, both because tree-of-heaven resprouts aggressively from cut stumps if not treated correctly, and because misidentifying it (sumac and young tree-of-heaven are genuinely easy to confuse) means removing the wrong tree and leaving the real host standing. If you’re not sure what’s growing at your property line, or you’re seeing heavy feeding activity on a valuable tree, it’s worth having an ISA Certified Arborist take a look before egg-laying season starts.
Ready to have an ISA Certified Arborist take a look? Schedule your free estimate today.