In 2002, one of the most destructive insects in North American history — the emerald ash borer (EAB) — was first discovered in the United States. Within 10 years, it had spread all the way to Eastern Massachusetts, having left millions of dead trees it had left in its wake and placing our own ash trees at risk.
But this isn’t a history lesson. It’s a current events story.
Fast forward to the current day and EAB remains a serious problem for homeowners, municipalities, and our region’s remaining ash trees. Untreated ash trees are still dying every year, even in communities where EAB has been established for more than a decade.
Fortunately, effective treatment options are available, and when implemented early, they can protect ash trees for decades to come.
Emerald Ash Borer: The Basics
Emerald ash borer (Agrilus planipennis) is a small, metallic-green beetle, measuring about half an inch in length. But it’s not the adult insects that are the problem. They do feed on ash tree foliage, but they don’t consume enough to seriously harm the trees.
Instead, it’s the larvae that cause the real trouble.
After they hatch from eggs deposited on the bark of ash trees, the larvae tunnel beneath the surface and begin feeding on the trees’ xylem and phloem — the tissue responsible for transporting water and nutrients, respectively. Their feeding behavior gradually girdles the tree and prevents it from functioning normally.
Unfortunately, EAB infestations are almost always fatal if left untreated. In fact, untreated ash trees have mortality rates approaching 100 percent once they become infested.
Which Trees Are Vulnerable to Emerald Ash Borer?
Unfortunately, EAB isn’t particularly selective. Nearly all North American ash species are susceptible to infestation, and untreated trees are likely to die once the insect becomes established.
This includes all four species commonly seen in Eastern Massachusetts:
- White Ash (Fraxinus americana)
- Green Ash (Fraxinus pennsylvanica)
- Black Ash (Fraxinus nigra)
- Blue Ash (Fraxinus quadrangulata)
It’s also important to understand that tree size doesn’t provide protection. EAB attacks ash trees ranging from young landscape specimens to mature shade trees that were planted decades ago.
The Symptoms of Emerald Ash Borer
One of the most challenging aspects of EAB management is that infestations often go unnoticed during their early stages.
By the time obvious symptoms begin to appear, the insects may have already been feeding beneath the bark for several years. That’s why the best course of action is to proactively treat ash trees before you even notice symptoms.
Nevertheless, treatments can still be effective if initiated promptly, at the first signs of trouble. So, if you decide not to treat your ash trees proactively, be sure to keep an eye out for any of the following:
- Thinning or Dying Canopy: One of the earliest and most noticeable symptoms is thinning foliage in the upper portions of the canopy. As the tree’s vascular system becomes compromised, branches begin to decline and die.
- Epicormic Sprouting: Ash trees frequently produce clusters of shoots along the trunk or larger branches in response to stress. These sprouts are essentially the tree’s last-ditch attempt to replace lost foliage.
- D-Shaped Exit Holes: Adult EABs leave small, D-shaped exit holes, measuring approximately one-eighth of an inch wide, when they emerge from beneath the bark. These holes are considered one of the hallmark signs of an infestation.
- Bark Splitting: Vertical splits may develop in the bark as the tree responds to larval feeding beneath the surface. In some cases, these cracks reveal the winding galleries created by EAB larvae.
- Woodpecker Activity: Woodpeckers are often attracted to infested ash trees and may remove patches of bark while searching for larvae. Increased woodpecker activity can sometimes alert homeowners to an infestation before other symptoms become obvious.
- S-Shaped Feeding Galleries: If the bark is removed, EAB larvae leave distinctive serpentine galleries packed with fine sawdust-like frass. These galleries disrupt the flow of water and nutrients throughout the tree.
Always contact a certified arborist promptly if you notice any of these signs. Early intervention remains the best way to preserve valuable ash trees.
Treatment Options: Protecting Your Ash Trees
The good news is that EAB is one of the few invasive tree pests that can often be managed very successfully. But you must initiate treatment before significant decline occurs.
The two most common treatment options include:
- Trunk Injections: Widely considered the gold standard for EAB management, trunk injections deliver systemic insecticides directly into the tree’s vascular system. These treatments are highly effective, but they must be readministered every two to three years.
- Soil Treatments: Some systemic insecticides can be applied as soil drenches or injections around the base of smaller ash trees. Once absorbed by the roots, the treatment is distributed throughout the tree and helps protect it from feeding larvae.
While treatment can be remarkably successful, timing matters. Trees that have already lost a significant portion of their canopy may be too far gone to save.
Emerald Ash Borers: FAQ
The EAB has been killing ash trees across Massachusetts for more than a decade, but many homeowners are still surprised to learn their seemingly healthy trees may be at risk. The answers below address some of the most common questions we hear about EAB treatment and ash tree preservation.
Can emerald ash borer kill a healthy ash tree?
Yes. EABs often attack healthy ash trees as readily as they do stressed or declining ones. Without treatment, most North American ash trees eventually die once they become infested.
How long does it take emerald ash borer to kill an ash tree?
The timeline varies depending on factors such as tree size, overall health, and the severity of the infestation. However, many untreated ash trees die within two to four years of becoming infested.
Can an ash tree recover from emerald ash borer?
In some cases, yes. Ash trees that are treated before they suffer significant canopy loss often respond very well to treatment. However, trees that have declined substantially may not recover, even with treatment.
Should I treat my ash tree if it still looks healthy?
Absolutely. EAB infestations often remain hidden for several years before symptoms become obvious. Waiting until an ash tree looks unhealthy can significantly reduce the likelihood of successful treatment.
Are emerald ash borer treatments worth the cost?
For many homeowners, preserving a mature ash tree is considerably less expensive than removing and replacing it. Treatment is often a cost-effective option, particularly for large, healthy trees that provide shade, privacy, and aesthetic value.
Can emerald ash borer spread from one ash tree to another?
Yes. Adult beetles naturally disperse in search of suitable host trees, which is why EAB spreads steadily throughout affected communities.
How do I know if my tree is an ash tree?
Ash trees are relatively easy to identify once you know what to look for. They typically have opposite (rather than alternate) branching patterns and compound leaves made up of several leaflets. If you’re unsure whether the tree on your property is an ash, a certified arborist can help identify it and recommend the appropriate next steps.
Protect Your Ash Trees Before It’s Too Late
EAB isn’t going away, and waiting until your ash tree begins to decline can significantly reduce the likelihood of successful treatment. Fortunately, proactive management can protect valuable ash trees for decades — even in communities where the pest has been present for years.
If you have an ash tree on your property, now is the time to have it evaluated. The sooner treatment begins, the better your chances of preserving the beauty, shade, and value your tree provides.
Contact us today to get started!
Sources and References
- USDA National Invasive Species Information Center – “Emerald Ash Borer”
Federal species profile of emerald ash borer (Agrilus planipennis) summarizing its native range, 2002 U.S. introduction, and tree impact, with an extensive directory of state, federal, and academic resources.
https://www.invasivespeciesinfo.gov/terrestrial/invertebrates/emerald-ash-borer - Forest Ecology and Management – “Ash Survival and Growth in Response to Emerald Ash Borer Invasion in Massachusetts Riparian Forests: Impacts of Biological Control”
Peer-reviewed study assessing ash mortality and the effects of early parasitoid biocontrol releases across six Massachusetts floodplain forests.
https://www.sciencedirect.com/science/article/abs/pii/S0378112725004591 - Massachusetts DCR – “Emerald Ash Borer in Massachusetts”
State agency guide tracking EAB’s spread across Massachusetts, its quarantine and firewood restrictions, trapping and detection methods, and the state’s parasitoid biocontrol program.
https://www.mass.gov/guides/emerald-ash-borer-in-massachusetts - UMass Extension – “Emerald Ash Borer”
Extension fact sheet detailing EAB identification, life cycle, damage signs, and management, including biological control and systemic insecticide options for landscape ash.
https://www.umass.edu/agriculture-food-environment/landscape/fact-sheets/emerald-ash-borer - MassWoods (UMass Amherst) – “Managing Northeastern Forests Threatened by Emerald Ash Borer”
Landowner and forester guide covering ash ecology, silvicultural and preservation strategies, insecticide treatment of preservation patches, and Indigenous cultural connections to ash.
https://masswoods.org/sites/default/files/2025-09/managing-ne-forests-threatened-by-eab-web-ua.pdf