Emerald Ash Borer in Vermont: What to Do with Your Ash Trees

Emerald ash borer is no longer a future problem in Vermont. The invasive beetle is now active throughout most of the state, including Chittenden County, and many ash tree infestations go unnoticed until thinning canopies and dieback start becoming visible.

Last spring, Jericho officials confirmed emerald ash borer larvae beneath the bark of ash trees along Schillhammer Road — another sign of how quickly the insect continues spreading across Vermont. For homeowners, the question is no longer whether emerald ash borer will reach the area, but whether ash trees are still healthy enough to protect before significant decline begins.

Key Takeaways

• Emerald ash borer has been confirmed in 13 out of 14 Vermont counties, and untreated ash trees do not survive infestation.
• Trees with less than 50% canopy thinning can often be saved with treatment, while trees beyond that threshold are usually better candidates for removal.
• Early signs are subtle and can show up two to four years after a tree is first infested, including D-shaped exit holes, woodpecker flecking, and top-down canopy dieback.
• Both EAB-effective treatments require a licensed pesticide applicator, so DIY treatment isn’t a viable option.
• The treatment window opens in May, which means a professional assessment in early spring is the first step.

Why Is the Emerald Ash Borer a Threat to Vermont Ash Trees?

Emerald ash borer (Agrilus planipennis) is a small, metallic-green beetle native to eastern Asia that kills North American ash trees by tunneling through the inner bark and cutting off the tree’s flow of water and nutrients. First detected in Michigan in 2002, EAB reached Vermont in 2018 and has now killed hundreds of millions of ash trees across more than 30 states.

Three things make EAB different from the average tree pest:

• It Targets All Native Ash Species: White, green, and black ash — the three ash species native to Vermont — are all vulnerable, and there are no known resistant varieties.
• It’s Nearly Always Fatal Without Treatment: Once infested, more than 99% of untreated ash trees die within 3-5 years.
• It Hides for Years Before Showing Symptoms: Trees can be infested for 2-4 years before any visible signs appear, which is why a tree that looks fine doesn’t mean it’s healthy.

How Do You Know if Your Ash Tree Has Emerald Ash Borer?

Knowing whether your ash tree has EAB comes down to looking in the right places at the right time of year — most of the early evidence appears high in the canopy and on the upper trunk, where it’s easy to miss from the ground. A trained eye can usually confirm an infestation from a combination of two or three indicators but spotting the first one is what gets the process started.

Watch for changes that start at the top of the tree and work downward:

• Top-Down Canopy Thinning or Dieback: Upper-canopy branches lose leaves and die off first, while the lower tree may still look relatively healthy.
• Woodpecker Flecking High in the Tree: Light-colored patches where woodpeckers have stripped bark to feed on larvae underneath — often the earliest visible sign.
• Vertical Bark Splits: Cracks running up and down the trunk where the tree is trying to callus over the larval galleries underneath.
• D-Shaped Exit Holes: About 1/8 inch wide with one flat side — facing any direction. Round holes indicate a different (usually native) borer; D-shaped holes mean EAB.
• S-Shaped Galleries Under the Bark: Winding tunnels packed with frass (fine sawdust mixed with insect waste). Usually only visible if a piece of bark falls off or is pulled back.
• Epicormic Sprouting: New shoots growing directly from the trunk or main branches — a stress response as the tree compensates for losing its upper foliage.

Spotting two or three of these indicators on the same tree is a strong signal of EAB, but several Vermont pests and diseases mimic individual symptoms, so a professional EAB assessment is the surest way to confirm what’s happening — and to figure out whether your tree can still be saved.

What Does Professional EAB Treatment Involve?

Professional EAB treatment uses systemic insecticides — either azadirachtin or mectinite — applied by a licensed pesticide applicator while the tree still has enough living tissue to absorb and distribute the treatment. The two treatments differ mainly in frequency and delivery method, and your arborist will recommend the right one based on the tree’s size, condition, and location:

• Azadirachtin: Needs to be reapplied every year, which makes it a steadier ongoing commitment at a lower cost per treatment.
• Mectinite: Delivered through small injection ports in the trunk and protects the tree for at least two full seasons per application, which often makes it the better fit for larger ash trees that justify the longer interval.

Both treatments are most effective when applied between spring bud break and late June, while the tree is actively moving water and nutrients through its trunk. Fall applications aren’t recommended in Vermont, which is why an early-spring assessment is the most important step in protecting your ash tree.

Should You Treat or Remove an Ash Tree with Emerald Ash Borer?

Not every ash tree affected by emerald ash borer needs to be removed immediately. The right decision usually depends on the tree’s health, location, condition, and overall value to the property.

Ash Trees That Are Often Worth Treating

Treatment may still make sense when a tree:

• Still has a relatively full, healthy canopy
• Shows only limited signs of decline or dieback
• Provides important shade, privacy, or erosion control
• Has sentimental or landscape value
• Is structurally sound and safe to maintain
• Can be monitored and treated consistently over time

In many cases, preserving a mature ash tree is less expensive than removing and replacing one of similar size.

When Removal Is Often the Better Option

Removal is usually the safer choice when a tree has:

• Significant canopy thinning or large dead sections
• Extensive bark splitting or visible woodpecker activity
• Structural instability or major branch failure
• More advanced emerald ash borer damage
• A location near homes, driveways, sidewalks, power lines, or other high-risk targets

As ash trees decline, they often become brittle quickly, which can make delayed removal more hazardous and expensive.

When Should You Call an Arborist About Your Ash Tree?

If you have ash trees on your property, it’s worth scheduling an assessment before another emerald ash borer treatment season arrives — especially if you’ve noticed thinning canopies, dead branches, bark splitting, or nearby infestations. Early evaluations help homeowners understand whether a tree is still a good candidate for treatment before decline becomes more advanced.

An arborist assessment is especially helpful if:

• You Have Multiple Ash Trees and Need to Prioritize: An assessment helps you sort which trees are worth treating, which should be removed, and which can be monitored.
• You Want a Clear Answer Before May: Treatment scheduling fills up quickly once the window opens; an April assessment puts you ahead of the rush.
• You Inherited an Ash With Unknown History: A baseline evaluation tells you what you’re working with before any decisions get made.
• A Neighbor’s Ash Has Been Confirmed Infested: Adult beetles can fly up to half a mile, so nearby infestation is a meaningful risk signal for your own trees.

Frequently Asked Questions About Emerald Ash Borer in Vermont

How do I know if my tree is an ash tree?

Ash trees have opposite, compound leaves with five to nine leaflets and diamond-patterned bark on mature trunks. Vermont’s three native ash species — white, green, and black ash — are all vulnerable to EAB. If you’re not sure, your town’s tree warden or a Certified Arborist can identify the species during a property visit.

How does emerald ash borer spread?

EAB spreads two ways: adult beetles fly between trees from June through September, and infested firewood carries larvae into new areas when transported. Don’t move firewood off your property if you have or suspect EAB. This is also why cutting down one ash doesn’t protect the others — the beetle moves through the air, not the soil.

What time of year is EAB most active in Vermont?

Adult beetles emerge and fly between June 1 and September 30, and eggs hatch in late summer with larvae feeding under the bark through fall. Treatments need to be applied before the beetles take flight, which is why the May treatment window matters.

What can I do with the wood from an ash tree that has to be removed?

The wood can stay on your property as firewood or mulch, or your arborist can chip it on-site and haul the debris to a permitted disposal site. Moving ash wood off your property isn’t an option — Vermont’s EAB quarantine restricts transporting it because infested wood is one of the main ways the beetle spreads.

Can I treat my ash tree myself?

No. Both EAB-effective treatment options require a licensed pesticide applicator. Over-the-counter products use lower-concentration formulations and improper application can injure the tree or fail to provide real protection. An on-site assessment by a Certified Arborist is the necessary first step.

Schedule Your Ash Tree Assessment Before This Treatment Season

The question isn’t whether EAB has reached your part of Vermont — it’s which of your ash trees can still be saved, and that answer doesn’t come from a search engine or a guess from the driveway. It comes from someone walking your property, looking up into the canopy, and pulling back the bark where it counts.

Teachers Tree Service has been helping homeowners across Chittenden County and throughout Northwestern Vermont answer that question tree by tree, with honest evaluations and clear recommendations for over 20 years. Call 802-922-3428 or request a proposal to schedule your on-site assessment, and you’ll know exactly where your ash trees stand.