By now, you’ve probably heard of the emerald ash borer (EAB) — one of the most destructive forest pests ever introduced to North America.
Since first being discovered in the United States in 2002, this invasive insect has killed tens of millions of ash trees, fundamentally altering forests, neighborhoods, and landscapes across the eastern half of the country.
And that unfortunately includes Maryland.
Having been first documented in the state in 2003 and established shortly thereafter, EAB threatens nearly every untreated ash in our region. But it’s important to know that you can still protect your tree, provided that it hasn’t yet become heavily infested and you act quickly.
Below, we’ll explain what emerald ash borer is, the warning signs of an infestation, and the treatment options available.
What Is Emerald Ash Borer?
Emerald ash borer (Agrilus planipennis) is a small metallic-green beetle native to Asia. Although it is relatively harmless in its native range, our native ash trees have few natural defenses against it, leaving them at high risk.
Adult beetles feed on ash foliage, but this causes very little damage — otherwise healthy trees can generally tolerate some leaf loss. The real threat comes from the larvae.
After EAB eggs hatch, the larvae tunnel beneath the bark of an ash tree and feed on its phloem and cambium, creating distinctive S-shaped galleries in the process. These tunnels disrupt the movement of water and nutrients throughout the tree, eventually causing canopy decline and death in most cases.
Because EAB spends most of its life hidden beneath the bark, infestations often go unnoticed until the tree begins showing visible signs of decline. This is one of the reasons regular inspections by an ISA Certified Arborist are so valuable.
Which Ash Trees Are at Risk?
Unfortunately, EAB attacks all native North American ash species, and virtually every untreated ash tree in Maryland is considered susceptible. Some of the ash species most commonly found in Maryland include:
- White Ash (Fraxinus americana): Once one of Maryland’s most common and valuable native hardwoods, white ash is highly susceptible to emerald ash borer.
- Green Ash (Fraxinus pennsylvanica): Frequently planted as a shade tree and naturally common in floodplains and other moist sites, green ash is also highly susceptible to infestation.
- Pumpkin Ash (Fraxinus profunda): Found primarily in wetlands and low-lying areas, pumpkin ash is readily attacked by emerald ash borer.
- Black Ash (Fraxinus nigra): Although restricted to our state’s cooler northern wetlands, black ash is among the most susceptible North American ash species.
- Blue Ash (Fraxinus quadrangulata): Rare in Maryland, blue ash appears somewhat more resistant to EAB than other ash species. However, it is not immune and can still become infested.
No matter which ash species you have, early detection is critical. Trees treated before they develop significant canopy decline often have the best chance of long-term survival, while heavily infested trees are usually doomed by the time obvious symptoms appear.
Symptoms of Emerald Ash Borer
One of the biggest challenges posed by EAB is that trees often appear healthy during the early stages of an infestation. And because the larvae spend most of their lives hidden beneath the bark, visible symptoms typically don’t develop until significant internal damage has already occurred.
Fortunately, there are several warning signs homeowners can watch for. While none of these symptoms alone confirms an EAB infestation, they should all prompt you to contact a plant health care expert.
- Canopy Thinning: As EAB larvae disrupt the tree’s ability to transport water and nutrients, the upper branches often begin producing fewer and smaller leaves. Over time, sections of the canopy may die back entirely, usually beginning near the top of the tree.
- Epicormic Sprouts: Stressed ash trees often respond to EAB attacks by producing clusters of new shoots along the trunk or major branches. Known as epicormic sprouts, these shoots represent the tree’s attempt to replace foliage lost higher in the canopy.
- Increased Woodpecker Activity: Woodpeckers are among the first animals to detect emerald ash borer infestations. As they search for larvae beneath the bark, they may remove patches of the outer bark, leaving behind light-colored scars that create a distinctive “blonding” appearance.
- D-Shaped Exit Holes: After completing their development beneath the bark, adult
EABs emerge through small, D-shaped exit holes measuring about one-eighth of an inch across. While they’re a classic sign of EAB, they rarely appear until an infestation is well established. - S-Shaped Larval Galleries: Winding, S-shaped tunnels etched into the wood by feeding larvae are often visible beneath the bark of trees under attack. These galleries disrupt the tree’s vascular tissues and are considered one of the most reliable indicators of an infestation.
- Bark Splitting: As larval galleries expand beneath the bark, the bark may begin splitting vertically. These cracks sometimes expose the winding galleries underneath or even reveal developing larvae hidden within the tree.
- Tree Death: Death hardly seems like a “symptom,” but the fact remains that without treatment, emerald ash borer is almost always fatal. Most untreated ash trees die within about two to five years of becoming infested, although the exact timeline depends on a variety of factors.
Emerald Ash Borer Treatments
Unfortunately, there is no cure for emerald ash borer once an infestation becomes advanced. However, many ash trees can be successfully protected if the problem is identified early and appropriate treatment begins before the tree has suffered extensive damage.
A few of the ways Baker Tree Service can help include:
- Inspecting Your Trees: Regular inspections provide the best opportunity to detect emerald ash borer before serious damage occurs. Early detection allows you to make informed decisions while treatment is still a viable option.
- Administering Systemic Insecticide Treatments: When administered before an attack or during the earliest stages of an infestation, emamectin benzoate trunk injections are currently considered the most effective treatment for protecting ash trees from EAB.
- Removing Hazardous Trees: When emerald ash borer has caused extensive decline, removal is often the safest and most cost-effective solution. Dead and dying ash trees become increasingly brittle over time, making them more likely to lose limbs or fail completely.
Every property is different, and there is no one-size-fits-all approach to emerald ash borer management. But our pest and disease specialists can assess the condition of your ash trees, determine whether treatment is likely to be successful, and recommend an appropriate management strategy.
The Emerald Ash Borer in Maryland: FAQ
EAB has become one of the most significant threats facing Maryland’s forests and landscapes. Below are answers to some of the questions we hear most often from homeowners who’re concerned about these pests.
What is emerald ash borer?
Emerald ash borer (EAB) is a small metallic-green beetle that attacks ash trees. While adult beetles cause very little damage, their larvae feed beneath the bark, disrupting the tree’s ability to transport water and nutrients. Left untreated, most infested ash trees eventually die.
Is emerald ash borer found throughout Maryland?
Yes. EAB is now established throughout Maryland, including the Eastern Shore. As a result, nearly every untreated ash tree in the state is considered vulnerable to infestation.
Can an ash tree survive emerald ash borer?
Yes, but timing is crucial. Trees that are healthy or only lightly infested can often be protected with systemic insecticide treatments. Once a tree has experienced significant canopy decline, however, treatment is much less likely to succeed.
How can I tell if my tree has emerald ash borer?
Common signs of EAB include canopy thinning, dead branches, epicormic sprouts growing from the trunk, increased woodpecker activity, D-shaped exit holes, bark splitting, and S-shaped galleries beneath the bark.
Should I treat my EAB-infested ash tree or remove it?
That depends on the tree’s condition, size, location, and overall value. Many healthy ash trees are excellent candidates for treatment, while trees with extensive decline or structural concerns are often better removed. An ISA-certified arborist can help you determine the most appropriate option.
How long does treatment last?
The most commonly used trunk-injection treatments provide protection for multiple years, though the exact interval depends on the product used and your arborist’s recommendations. Periodic retreatment is typically necessary to maintain protection.
Can emerald ash borer spread to other kinds of trees?
No. EAB attacks only ash trees (Fraxinus spp.). Although adult beetles may occasionally land on other tree species, they do not reproduce or complete their life cycle on non-ash trees.
Protect Your Ash Trees While You Still Can
Even though EAB has spread across our state, you don’t have to sit by and watch your ash die. With regular inspections and timely treatment, many healthy, high-value ash trees can continue thriving for years.
The ISA Certified Arborists at Baker Tree Services can evaluate your ash trees and recommend the most effective management strategy for your property. Whether your tree is a good candidate for treatment or should be removed before it becomes hazardous, we’ll help you make an informed decision.
Contact us today to schedule an evaluation and protect your ash trees while there’s still time.
Sources and References
- Maryland Department of Agriculture – “Emerald Ash Borer”
State agency page on EAB in Maryland, covering the pest’s arrival and impact, economic threat to ash and the nursery industry, and MDA’s monitoring, trapping, treatment, and parasitoid-release programs.
https://mda.maryland.gov/plants-pests/pages/eab.aspx - University of Maryland Extension – “Emerald Ash Borer (EAB)”
Extension fact sheet on EAB identification, detection signs, treatment-versus-removal decisions, and homeowner guidance, noting the pest is now well established statewide including the Eastern Shore.
https://extension.umd.edu/resource/emerald-ash-borer-eab - Maryland DNR – “Emerald Ash Borer” (Homeowner response guide)
Forestry-service guide walking landowners and communities through EAB response: tree inventory, treatment with emamectin benzoate, proactive versus reactive removal, replanting, wood utilization, and biocontrol.
https://dnr.maryland.gov/forests/documents/emeraldashborer.pdf