Short answer
Scrape them off and kill them. Philadelphia's lanternfly guidance says to scrape egg masses into a bag or container of rubbing alcohol, or crush them, and that masses can be found from September through June. On a fence, use a plastic scraper or old card on vinyl and aluminum and a putty knife on wood, and check the undersides of rails and the back of gate frames, where masses are easy to miss.
Why fences around Boyertown and Oley get them
Spotted lanternfly was first found in the United States in Berks County in 2014, and the first quarantine covered Pike and District townships, the hill country between Oley and Boyertown. The insect has spread a long way since then, but the Pike and District area has had it longer than anywhere else in the country.
Females lay egg masses from October onward on sheltered outdoor surfaces. A fence offers plenty of those: the shaded side of a privacy fence that faces a wood line, the bottom edge of a rail, the inside of a gate frame and the stack of spare pickets behind the shed. Each mass holds roughly 30 to 50 eggs, so missing one under a rail matters.
What an egg mass looks like on a fence
Fresh masses look like a smear of gray mud or putty about an inch or so long. Older ones dry out and crack, and you can sometimes see rows of seed-like eggs where the coating has flaked off. On weathered gray cedar or pressure-treated pine they blend in well. On white or tan vinyl they are easier to spot, though only when you look at the right spots.
Where to look on each kind of fence
| Fence type | Check here first |
|---|---|
| Wood privacy or board-on-board | Underside of the bottom rail, behind the backer rails, post caps, the side facing the woods |
| Vinyl privacy | Under the top rail lip, in the gap where pickets meet the bottom rail, behind gate hardware |
| Aluminum or steel ornamental | Inside the U-channel of the rails, behind hinge and latch brackets |
| Split rail | The underside of each rail where it enters the post mortise |
| Chain link | Top rail, terminal post caps, tension bands and any privacy slats |
How to scrape without damaging the fence
- Hold a zip-top bag or small jar with an inch of rubbing alcohol under the mass.
- On vinyl, aluminum and coated chain link, use a plastic scraper, an old gift card or a plastic putty knife. Steel blades can scratch powder coat and leave gouges in vinyl that hold dirt.
- On wood, a metal putty knife is fine. Work with the grain so you don't lift fibers.
- Push the mass off the edge into the alcohol, seal the bag and put it in the trash.
- If you can't catch it, crush it thoroughly against the fence or the ground. The Philadelphia guidance lists crushing as an option, so a smear is acceptable on a fence you plan to wash anyway.
Can I just pressure wash them off?
We don't rely on it. The published guidance names scraping into alcohol and crushing, not washing, so a pressure washer may simply move live eggs onto the lawn or the mulch bed. A pressure washer can also do more harm to the fence than the insects do: high pressure raises the grain on cedar and pine, can etch soft vinyl, and drives water behind post caps. If you wash a fence for other reasons, scrape first and use a wide fan tip at low pressure.
Do lanternflies damage the fence itself?
The eggs don't eat into wood or vinyl. The nuisance on fences is mostly what comes later: the adults gather on nearby trees and vines and drip a sticky honeydew that can grow black sooty mold on whatever sits below. A fence line running under infested trees can turn gray and tacky by late summer. That washes off vinyl and aluminum with mild soap and water. On wood, it can shorten the time before the fence needs cleaning and a fresh coat of stain.
A note for new fence projects in the fall
Fall is a popular time to install fences in Berks and western Montgomery County, and it overlaps with egg-laying season. If old panels are coming down, check them before they're hauled off or reused. If lumber or panels sit in the driveway for a few days before installation, take a quick look along the edges before they go up. A fresh fence is the easiest one to check, and the cheapest time to catch a mass is before it hatches in spring.
We're happy to point out egg masses we spot during an estimate or repair visit. If they're on a fence we're replacing anyway, they leave with the old material.
Common questions
When is the best time to scrape egg masses off a fence?
Any time from late fall through early spring, before they hatch. Philadelphia's guidance says masses can be found from September through June, so a check in November and another in March covers most of the season.
Will stain or paint over an egg mass kill it?
We wouldn't count on it, and it leaves a lump in the finish. Scrape the mass off first, then stain or paint.
Should I report egg masses I find?
Reporting rules and quarantine programs have changed over the years. Check the Pennsylvania Department of Agriculture's current lanternfly page for what it asks residents to do now.