Emerald Ash Borer in New Jersey: What Every Homeowner Needs to Know
Emerald ash borer is an invasive beetle that has killed hundreds of millions of ash trees across North America since arriving from Asia in the early 2000s. In New Jersey, an infested ash tree usually shows top-down canopy thinning first, followed by S-shaped tunnels under loose bark, small D-shaped exit holes, and heavy woodpecker activity. Most infested ash trees die within 2 to 4 years of visible symptoms. Treatment with systemic insecticides can save trees caught early; trees with more than 30 to 50 percent canopy loss are usually past the treatment threshold and removal is the safer call. Dead ash trees deteriorate faster than most other species in NJ, so action should not be delayed.
If you have an ash tree on your property, pay attention.
The emerald ash borer is an invasive beetle that has killed hundreds of millions of ash trees across North America since it arrived from Asia in the early 2000s. It spread into New Jersey and has been working through our counties ever since.
An ash tree that looks fine today can be dead within two to three years of infestation. And a dead ash tree on a residential property is a serious hazard. The wood deteriorates fast. Branches fail without warning. The trunk can go.
Here's what to look for and what to do about it.
What Is the Emerald Ash Borer?
The emerald ash borer (Agrilus planipennis) is a small metallic green beetle, roughly half an inch long. The adult beetles feed on ash leaves, which causes minor surface damage. The real destruction comes from what happens next.
Females lay eggs in the bark and the larvae hatch beneath it. Those larvae burrow under the bark and feed on the layer of tissue that moves water and nutrients up and down the tree. This cuts off the tree's supply lines. The damage starts slowly, then accelerates. By the time most homeowners notice something is wrong, the infestation is usually well advanced.
Signs Your Ash Tree Has Emerald Ash Borer
Thinning canopy starting at the top. The first visible sign is usually dieback at the crown. The top of the tree loses leaves and branches before the lower canopy shows damage. This top-down dieback pattern, on an ash tree specifically, is a strong indicator.
S-shaped galleries under the bark. If you peel back a section of loose or peeling bark, you'll see winding S-shaped tunnels carved by feeding larvae. These galleries are a definitive sign of ash borer activity.
D-shaped exit holes. When adult beetles emerge from the tree each spring, they chew out through the bark and leave small D-shaped holes roughly the size of a pencil eraser. Finding several of these on the trunk or main branches confirms an active infestation.
Sprouting from the lower trunk and roots. Called epicormic sprouting, this is the tree's stress response. It shoots out small leafy branches from the lower trunk and root flare as it tries to push growth below the point of damage. A lot of this low-level sprouting on an otherwise thinning ash tree is a clear warning sign.
Heavy woodpecker activity. Woodpeckers feed on ash borer larvae under the bark. If you're seeing a lot of woodpecker damage on the upper portion of an ash tree's trunk, there's likely a good larval population underneath.
broader signs of tree decline beyond ash borer
How to Identify an Ash Tree in New Jersey
Not every homeowner knows what kind of trees they have. Here's how to identify ash.
Ash trees have compound leaves, meaning each leaf is actually a central stem with multiple leaflets attached to it. Most New Jersey ash trees carry between five and nine leaflets per leaf. The bark on mature ash trees has a distinctive diamond-shaped pattern that becomes more pronounced as the tree ages.
White ash and green ash are the two most common species in residential and municipal settings across Morris, Essex, Passaic, Sussex, and Bergen County. Both are fully susceptible to emerald ash borer.
Ash tree removal in New Jersey
What Are Your Options?
Treatment. If the tree is caught early and is otherwise in reasonable health, insecticide injection treatment can slow or halt the infestation and allow the tree to recover. This has to be applied by a licensed applicator and has to happen before the tree declines too far. Once more than 30 to 50 percent of the canopy is already gone, treatment is generally not worth pursuing.
Removal. If the tree is past the point where treatment makes sense, removal is the responsible move. An ash tree killed by emerald ash borer does not hold up safely for long. The wood goes brittle. Branches fail in ways that are hard to predict. These are not trees you want standing over a house, a driveway, a power line, or anywhere people walk.
We remove ash trees across North and Central New Jersey regularly. The typical ash borer victim in a residential yard is 40 to 60 feet tall, close to structures, and in exactly the kind of location that requires the right equipment and an experienced crew.
Ash tree removal services in North Jersey See what ash tree removal costs in New Jersey Get a free estimate on your ash tree ash removal pricing details
What About Moving the Wood?
New Jersey has had regulations in place on moving ash wood products to slow the spread of emerald ash borer into areas not yet affected. When we remove an ash tree from your property, we handle all debris disposal. You don't need to manage how or where the wood gets transported. That's our job.
What Happens After the Tree Comes Down?
You'll have a stump. Stump grinding is the standard option for most residential properties. It chips the visible stump down below grade so you can restore the area.
Stump grinding in New Jersey Stump grinding vs. stump removal: which one do you need?
How Ash Borer Compares to Other NJ Tree Pests
Emerald ash borer is the most lethal tree pest currently active in NJ on a single species. It almost always kills the ash trees it infests. Spotted lanternfly is a wider-impact pest that hits 70+ species but rarely kills healthy trees outright. Twolined chestnut borer hits stressed oaks specifically. Spongy moth caterpillars defoliate oaks during May and June.
What this means for a homeowner with mixed species on the property: each pest has its own monitoring schedule and response. Ash borer should be checked every spring on any ash tree, regardless of how the tree looked last year. Lanternfly egg masses should be scraped off in winter. Oak symptoms get watched in summer.
A property walk in late spring catches most issues across all four pests at the same time.
the other invasive pest hitting NJ trees
When and How to Prune Around an Ash Borer Diagnosis
If an ash tree is confirmed to have emerald ash borer but is still in early-stage infestation (less than 30 percent canopy loss), targeted pruning of dead wood reduces fall risk while treatment is underway. The pruning should happen outside the active beetle flight period (roughly May through September), so late fall or winter cuts are safer.
If the tree is past the treatment threshold, pruning is usually a waste of time and money. The decline accelerates regardless. Removal scheduling becomes the priority.
For neighboring ash trees on the same property that look healthy, a preventative treatment program can buy years of life. A licensed pest control operator handles the actual treatment.
when to prune ash and other species summer care during active borer season
Don't Wait on This One
Ash borer doesn't get better on its own. A tree that's 20 percent affected today can be fully dead in 18 months. And a dead ash deteriorates faster than most other species we deal with in New Jersey.
If you have ash trees on your property and haven't had them assessed recently, now is a good time to do it.
Request a free assessment of your ash trees We serve all of North and Central New Jersey