What Is the Emerald Ash Borer?
The emerald ash borer (Agrilus planipennis) is an invasive insect native to Asia that arrived in Minnesota around 1990. It’s a small, metallic-green beetle — and despite how pretty it sounds, it’s anything but harmless. EAB is the most destructive and costly forest insect to ever have invaded North America.
EAB was first discovered in Minnesota in 2009. The insect larvae kill ash trees by tunneling under the bark and feeding on the part of the tree that moves nutrients up and down the trunk. In other words, the beetle essentially cuts off the tree’s circulatory system from the inside — and the tree slowly starves.
Here’s the scope of the problem in Minnesota specifically: Minnesota has one of the largest ash populations in the country, with close to one billion ash trees in cities and forests. Losing these ash trees can have extreme ecological consequences on our urban tree canopies and forest ecosystems.
~1BAsh trees in MN at risk58+MN counties with EAB confirmed2009Year EAB first found in MN2–4 yrsTime to kill an untreated treeAnd it keeps spreading. The Minnesota Department of Agriculture (MDA) has confirmed EAB in multiple new locations as recently as 2025, with EAB found for the first time in Meeker, Murray, Ottertail, and Wadena counties — bringing the total to 58 counties in the state. That’s two-thirds of Minnesota’s 87 counties.
Still not sure if you have ash trees? Ash trees are easy to identify — they have compound leaves with several small leaflets arranged in opposite pairs along a single stem, and their bark develops a distinctive diamond-ridge pattern as the tree matures. If you’re unsure, an tree care specialist can identify your trees quickly.
Signs of an EAB Infestation
One of the most frustrating things about EAB is that most of the emerald ash borer life cycle takes place below the bark, and symptoms might not appear until more than four years after infestation. By the time you notice something obvious, the damage may already be severe. That’s why knowing the specific signs to look for is so important.
Thinning & Dieback at the Top
The first symptom you will typically notice is dieback in the canopy of the tree. Smaller leaves and closer-spaced buds are also indicators of stress.
D-Shaped Exit Holes
Emerging adult beetles chew characteristic 1/8-inch-wide, D-shaped exit holes that can be useful in confirming infested ash trees. Look closely at the bark — these small, distinctive holes are a telltale giveaway.
Woodpecker Damage & Flecking
Woodpeckers readily probe for larvae feeding beneath the bark and often reveal infested trees during the winter months. These trees become covered in light-colored “flecking” as woodpeckers remove the outer bark.
S-Shaped Galleries Under the Bark
EAB tunneling can cause the bark to split open, revealing characteristic S-shaped galleries underneath — the winding feeding tunnels left behind by larvae as they eat through the tree’s inner bark.
Epicormic Shoots at the Base
Unusual sprouts growing at the base of the trunk or along the lower trunk — called epicormic shoots — are another sign the tree is in serious stress and struggling to survive the infestation.
Bark Splitting & Cracks
Vertical bark splits, especially in the upper half of the tree, can indicate EAB activity beneath the surface. Bark cracks combined with woodpecker damage in the tree canopy are tell-tale signs of possible EAB infestation and should be reported promptly.
Important: Examining a tree’s canopy is not a good method for detecting EAB on its own, as there are other causes for ash to decline. If you spot any of these signs, the best move is to have a tree care specialist confirm the infestation. The MDA also asks residents to report suspected EAB at their Report a Pest portal at mda.state.mn.us.
Why an Infested Tree Is a Genuine Safety Hazard
This is the part most homeowners underestimate. An ash tree showing early signs of EAB can look mostly fine from a distance. But what’s happening structurally is a different story — and it can turn dangerous faster than you’d expect.
The wood becomes brittle — quickly
Ash trees killed by emerald ash borer become extremely brittle and break easily as they decline. Branches can fall on people and property in snowstorms, with a light breeze, or even on a calm, clear day. Unlike some other tree species, ash has a thin ring of conducting tissue that supplies water through the entire tree. When EAB larvae damage that system, the structural failure can be rapid and unpredictable.
Decay fungi accelerate the danger
EAB carries several decay fungi that can quickly rot branches. The branches become hazardous to people, pets, and property if the tree is not removed. And once those fungi take hold, the deterioration isn’t always visible from the outside — meaning a tree that looks stable may actually be rotting from within.
Limbs — and the whole tree — can come down
Severely infested trees can lose limbs or topple over at any time, posing a danger to people and property below. If your ash is near a home, garage, fence, driveway, or anywhere people walk, this isn’t a risk worth sitting on. Infested trees in cities and near structures are usually removed because they pose a danger to people and property.
Waiting makes everything harder and more expensive
Here’s the practical reality: waiting to remove your tree once it has become heavily infested or dead will be more expensive because brittle ash trees are dangerous to cut down. A living tree is far easier — and cheaper — to remove safely than a dead one with compromised structural integrity.
Dead ash trees pose special dangers due to their extremely brittle wood, requiring careful removal procedures, like extensive rigging to prevent damage to nearby structures or injuries to crew. The sooner you act, the simpler the job — and the lower the cost.
Why You Should Hire a Professional — Not DIY This One
We get it. There’s a strong temptation to handle tree problems yourself but when it comes to EAB, professional expertise isn’t just a convenience — it’s always the safest choice
Removal of a compromised tree is legitimately dangerous work.
Tree removal often requires specialized equipment and is considered dangerous work — even more so in an urban environment, where structures, roads, powerlines, and people may be in the drop zone of the tree to be removed. Professional crews carry the training and insurance to protect you and your property.
If you have ash trees on your property, now is the time to be proactive. Have them evaluated by a tree care specialist. Know what you’re looking at and mitigate the risk.
Have questions about an ash tree on your property? Reach out to us — we’re happy to take a look and walk you through your options.
Don’t Wait Until It’s an Emergency
Contact us today for a professional assessment of your ash trees. We’ll help you understand your options, what can be saved, and safely remove what can’t.
Sources & Further ReadingMinnesota Department of Agriculture — Emerald Ash Borer Found in New Areas of Minnesota (June 2025)University of Minnesota Extension — Emerald Ash Borer in MinnesotaMinnesota DNR — Emerald Ash Borer (EAB)Minnesota DNR — Emerald Ash Borer ManagementCary Institute of Ecosystem Studies — 8 Billion North American Ash Trees at Risk from EABIowa State University Extension — Emerald Ash Borer — Yard and GardenPurdue University FNR Extension — Timely Tree Removal (EAB Brittleness)American Family Insurance — Homeowners Guide to EAB Treatment & PreventionScott SWCD — EAB Prevention and Management StrategiesMinnesota
