Is Emerald Ash Borer Still A Threat?

Adult beetles are still emerging from ash trees in 35 U.S. states and five Canadian provinces, killing untreated trees of every size. The metallic green beetle, Agrilus planipennis, has now been confirmed in more than 35 U.S. states and several Canadian provinces, with new county-level detections still arriving each season. Tens of millions of ash have already been lost, and roughly 8 billion native ash remain at risk on the continent.

The sections below walk you through where the beetle has spread, how to catch an infestation early, what treatments still work, and when removal is the smarter call.

The Outbreak That Reshaped North American Forests

A single detection near Detroit, Michigan, in the summer of 2002 marked the first time Agrilus planipennis was found outside its native range in eastern Asia. By the time foresters realized what they were looking at, the larvae had already tunneled under the bark of millions of ash trees across southeast Michigan.

Federal and state quarantines came too late to slow the spread, and within two decades the beetle colonized nearly the entire eastern and midwestern United States. That single delayed response is now a standard case study in invasion biology.

Why the Larvae, Not the Adults, Do the Real Damage

Adult beetles chew small notches in leaves during their brief four-to-six-week lifespan above ground, but that feeding rarely kills a tree. The destruction happens out of sight: larvae hatch from eggs laid on the bark, then bore inward and serpentine through the cambium, the living tissue just beneath the bark that carries water and nutrients.

By the time you see canopy thinning at the top of the tree, the larvae have already girdled most of the major branches from the inside. You can think of the cambium as a one-lane highway feeding the entire crown.

Once that highway is cut off, no amount of watering, pruning, or fertilization brings the tree back. That is why early detection and preventive insecticide use are the only proven strategies for keeping a healthy ash alive.

The Scale of What Remains at Risk

North America is home to an estimated 8 billion native ash trees across roughly 10 species, including green ash, white ash, black ash, and blue ash. Each species is susceptible to emerald ash borer at every life stage, from sapling to mature canopy tree. Because ash makes up a meaningful share of both urban street trees and wild riparian forests, the potential loss extends well beyond individual yards.

It reaches into watersheds, streamside shade, and the woodlots that supply baseball bats, tool handles, and commercial lumber. Your local creek banks and your son’s baseball glove are both downstream of this outbreak.

That reach, however, started in scattered pockets and spread unevenly, so mapping today’s footprint tells the full story.

Where Emerald Ash Borer Has Reached So Far

According to the USDA APHIS map and the Emerald Ash Borer Information Network, confirmed detections have crossed the Mississippi, jumped the Rockies into Colorado, and pushed south into Texas, Louisiana, Mississippi, Alabama, Georgia, and Florida. In Canada, the Canadian Food Inspection Agency has logged infestations in Ontario, Quebec, New Brunswick, Nova Scotia, Manitoba, Saskatchewan, and parts of Alberta.

The pattern since 2002 has been steady westward and southward expansion, with new county records added every field season by state departments of agriculture. You can expect one or two new counties near the leading edge each year, even in states already considered infested.

The 2024 Spread Snapshot

USDA APHIS and state forestry agencies confirmed new county-level detections in at least 14 states during 2024, pushing the cumulative infested range past 380,000 square miles. Counts shift as new detections are confirmed, so treat the table as a working summary rather than a final tally.

Why Quarantines Still Matter in Already-Infested States

If your state is already on the map, you might wonder why firewood and nursery-stock rules still apply. The answer is simple: emerald ash borer spreads primarily through human movement of ash wood, ash nursery stock, and untreated firewood. Quarantine regulations limit how far infested material can travel, which slows the jump between still-uninfested counties and gives foresters a few extra seasons of lead time.

Skipping those rules on a camping trip or a furniture move is exactly how the beetle keeps leapfrogging across long distances. Your next load of weekend firewood could be the one that starts a new county outbreak.

Recognizing the Early Warning Signs of Infestation

The hardest part of managing emerald ash borer damage to ash trees is that the most useful clues appear on the bark, not in the canopy. By the time the leaves thin at the top, the larvae have usually been feeding for two or three years. Walking around your tree once a season and looking at the trunk and lower limbs gives you a much earlier read than standing on the driveway and squinting at the upper branches.

The Three Diagnostic Signs Worth Memorizing

Three symptoms tend to show up first, and each one is worth a closer look during a quick inspection. None is diagnostic on its own, but seeing two or three together is a strong reason to call an arborist.

• ▸D-shaped exit holes: Adult beetles chew a tidy, half-circle opening roughly 3 to 4 millimeters wide as they emerge through the bark, leaving the single most reliable sign on the trunk.
• ▸S-shaped larval galleries: If bark flakes off and you see winding, serpentine tunnels packed with frass (a sawdust-like waste), larvae are still active underneath.
• ▸Epicormic shoots and canopy thinning: A dying ash often pushes out clusters of pale, weak sprouts along the trunk and major limbs, while the upper crown thins and yellows, a sign the cambium is already partly girdled.

Why Woodpecker Damage Often Shows Up First

Woodpeckers hunt emerald ash borer larvae by hammering through the bark, leaving the trunk flecked with pale, rectangular patches where outer bark has been stripped away. On an otherwise full-canopied ash, that bark flecking is often the very first clue a homeowner notices, sometimes a year or two before any leaf symptoms appear. If your ash looks healthy from a distance but the trunk looks like it was lightly chiseled, treat that as an early warning, not a curiosity.

The window between first infestation and tree death usually runs three to five years, and many homeowners miss it because they only look up. Spending ten minutes twice a year on bark-level inspection is the most effective habit for catching the problem while treatment is still an option.

Treatment Options That Can Still Save Healthy Ash Trees

If your ash is healthy, more than 30 percent of the canopy intact, and the trunk is still solid, chemical treatment is a proven path to keeping it alive. The two products that dominate arborist practice are soil-applied imidacloprid and trunk-injected emamectin benzoate. Both move through the tree’s vascular system and kill larvae as they feed inside the cambium.

Comparing the Two Standard Insecticide Options

Both products are restricted-use pesticides and must be applied by, or under the supervision of, a licensed applicator. Read the label carefully, follow state restrictions on flowering plants near treatment areas, and treat only trees that are healthy enough to recover. Imidacloprid is generally cheaper per application, while emamectin benzoate costs more up front but spreads the labor across a longer protection window.

The Cost and Commitment Side of Treatment

Treatment costs vary widely by region, tree size, and product choice, but a reasonable planning range runs $100 to $500 per tree per application. Multiply that across two or three applications over a decade, and a mature shade tree can easily reach $1,500 to $3,000 in lifetime insecticide costs.

The math works because losing a 50-year-old ash costs more in stump grinding, replanting, and lost property value than keeping it alive does. Run your own numbers before deciding, since your mileage will depend on local arborist rates and tree size.

“Treat on a calendar, not a reaction. Waiting for visible damage before starting is the single most common reason treatments fail, because the cambium is already gone by then.

Where Biological Control Fits

Three tiny parasitoid wasps, Oobius agrili, Tetrastichus planipennisi, and Spathius agrili, are being mass-reared and released across the infested range under the USDA-led biological control program. These wasps do not eliminate emerald ash borer, but in some sites they are slowly building toward population-level suppression, with parasitism rates rising year over year. Foresters now treat them as a long-term tool for wild populations rather than a quick fix for backyard trees.

Yet those same treatments fall flat on trees too damaged to justify the cost, which is why removal sometimes wins out.

When Removal Makes More Sense Than Treatment

Not every ash tree is worth fighting for. Once the canopy drops below roughly 30 percent, the trunk shows extensive bark loss, or woodpecker damage covers most of the trunk, treatment rarely turns the situation around. In those cases, removal is the safer and more economical call, both for the tree’s owner and for anyone walking beneath it.

How Municipalities Are Phasing Ash Out of Urban Canopies

Cities and towns across the Midwest and Northeast have been quietly rewriting their urban forestry management plans for over a decade. Many now avoid planting new ash on streets and boulevards, and most have aggressive removal schedules for ash larger than a certain diameter. The goal is to limit future liability: a dead ash near a sidewalk or playground is a lawsuit waiting to happen.

If your city has sent a notice about a street tree in front of your house, that policy shift is the reason. You can usually appeal the schedule with a recent arborist report, but expect the default answer to be removal.

Replacement Species That Fill the Same Role

A lost mature ash casts heavy shade that no single replacement matches overnight, so species such as white fringetree, swamp white oak, and hackberry are being planted to recover much of the same ecological and visual role without the borer vulnerability. Diversifying the canopy is the broader goal, so picking more than one replacement species is smarter than picking a single substitute.

• ▸Honeylocust (thornless cultivars): Open, dappled shade; tolerates urban soil and salt.
• ▸Kentucky coffeetree: Tough, drought-tolerant, large mature canopy for big yards.
• ▸Bur oak and swamp white oak: Long-lived natives that support far more native insects than ash ever did.
• ▸Hardy rubber tree (Eucommia): Glossy foliage, strong urban tolerance, underused in most regions.
• ▸Diverse maple cultivars: Including freemanii hybrids, which blend silver and red maple traits for fast shade without the worst of either species’ drawbacks.

Long-Term Outlook for Ash Trees and the Forests They Support

Ash mortality in infested forests is now measured in tens of millions of trees, and the ripple effects are visible in streamside erosion, declining woodpecker and cavity-nesting bird habitat, and the loss of ash-dependent native insects like the eastern tiger swallowtail caterpillar’s preferred host. Watershed function has changed too, because ash-lined streamsides used to slow runoff and stabilize banks with their dense, shallow root systems.

Are Ash Trees Still Dying From Emerald Ash Borer?

Yes, and new infestations continue to be confirmed in counties with no previous record. The pace of new detections has slowed in the long-infested core of the Midwest, but spread continues at the leading edges of the range. Anywhere an uninfested ash meets a vector, the clock restarts.

Has the Outbreak Been Controlled Anywhere?

No full eradication has occurred, and none is expected. The realistic goal is coexistence: keep high-value landscape trees alive with insecticide, accept loss in wild forests, and use biological control to gradually reduce beetle pressure. In a few long-infested sites, parasitoid populations appear to be stabilizing local emerald ash borer numbers, though scientists caution it is still early to call it a turning point.

““We are not going to eradicate emerald ash borer. The goal is to bring it into the ecological background, alongside native wood-boring beetles that rarely kill trees. That will take decades, not years.”, U.S. Forest Service research entomologist, summarizing the federal position in recent briefings.

The Realistic Timeline for Coexistence

Most forest entomologists working on this beetle expect decades, not years, before ash regains any meaningful share of the eastern canopy. In the meantime, the smartest moves for property owners are the boring ones: inspect your ash twice a year, treat healthy trees on a calendar, and remove the ones already in decline before they become a hazard.

That combination is what keeps a single yard, and a single town, ahead of the leading edge. Your own inspection habit matters more than any single federal program, because the front line really does run through individual properties.

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