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HOME / BLOG / EMERALD ASH BORER
[ FLAGSHIP · EAB · 7 MIN READ ]

How the Emerald Ash Borer Got Into Canada: Windsor Was Ground Zero

BY MATT DENEAU, ISA CERTIFIED ARBORIST
Emerald ash borer larval galleries carved under the bark of an ash tree
S-SHAPED LARVAL GALLERIES — HOW THE BORER GIRDLES AN ASH FROM THE INSIDE

The emerald ash borer arrived in Canada at Windsor, in the summer of 2002. It had already established itself across the river around Detroit, and it crossed. Most likely in wood packaging or pallets moving through the border, though nobody can point at a single shipment and say that one.

If you live in Windsor or anywhere in Essex County, you were living at the front edge of the worst tree die-off in Canadian history, and you probably did not know it for another five or six years.

Here is the part most people find hard to believe. By the time anyone identified the beetle in 2002, it had already been here for close to a decade. Researchers went back and read the growth rings in dead ash around Detroit and Windsor, and the damage traced to the early 1990s. So the discovery was not an arrival. It was somebody finally noticing.

INTERACTIVE — THE INVASION TIMELINETAP A YEAR
~1993 — The quiet arrival
Growth-ring analysis later traced the first damage around Detroit and Windsor to the early 1990s — nearly a decade before anyone knew.
2002 — Ground zero: Windsor
The beetle is formally identified in Windsor in summer 2002, having crossed from Detroit — likely in wood packaging or pallets. The discovery was not an arrival; it was somebody finally noticing.
2008 — Essex County losses mount
Windsor-Essex homeowners start seeing mass crown dieback. Municipalities begin budgeting for thousands of street-tree removals.
2013 — Ontario-wide
Confirmed infestations run from Essex County to Grey County and east to Ottawa, with jumps driven by firewood movement.
2020 — Six provinces, 30+ states
The Windsor entry point has become a continental infestation. Firewood restrictions remain in force.
2026 — The aftermath, here
Standing ash in Windsor-Essex today is almost never healthy — it's dead ash that hasn't come down yet, getting more brittle and more expensive every season.

Where the beetle came from

The emerald ash borer is native to Asia: China, Japan, Korea, Taiwan, Mongolia, and the Russian Far East. Over there it is a minor pest, because Asian ash species evolved alongside it and can fight it off.

North American ash never had to. Our trees had no defences, and the beetle had no predators here worth mentioning. That combination is why it moved the way it did.

How it spread out of Windsor

Adult beetles fly, but not far. Left alone, the infestation would have crept outward a few kilometres a year.

It did not creep. It jumped hundreds of kilometres at a time, because people moved firewood. Somebody cuts up a dead ash in Windsor, throws it in the truck, drives to a cottage north of Sault Ste. Marie, and the larvae overwintering in that wood emerge somewhere new the following spring.

From Windsor the beetle has since been confirmed across six provinces and more than thirty American states. Ontario infestations run from here up to Grey County and east to Ottawa, with separate pockets on Manitoulin Island and around Sault Ste. Marie.

Firewood movement restrictions are still in place for exactly this reason. They are worth taking seriously even now.

What happened to the ash trees

Roughly 99 percent mortality in an infested area within about eight to ten years. Not most of them. Effectively all of them.

INTERACTIVE — ASH SURVIVAL AFTER INFESTATION ARRIVESHOVER THE BARS
Y1
Y2
Y3
Y4
Y5
Y6
Y7
Y8
Y9
Y10
YEAR 1: ~98% OF ASH STILL ALIVE — Early infestation is nearly invisible — damage is under the bark years before the crown shows it.
YEAR 2: ~95% OF ASH STILL ALIVE — Early infestation is nearly invisible — damage is under the bark years before the crown shows it.
YEAR 3: ~88% OF ASH STILL ALIVE — Early infestation is nearly invisible — damage is under the bark years before the crown shows it.
YEAR 4: ~75% OF ASH STILL ALIVE — Early infestation is nearly invisible — damage is under the bark years before the crown shows it.
YEAR 5: ~55% OF ASH STILL ALIVE — The visible collapse years: crowns thin from the top down while trunks throw panic shoots low.
YEAR 6: ~35% OF ASH STILL ALIVE — The visible collapse years: crowns thin from the top down while trunks throw panic shoots low.
YEAR 7: ~18% OF ASH STILL ALIVE — The visible collapse years: crowns thin from the top down while trunks throw panic shoots low.
YEAR 8: ~8% OF ASH STILL ALIVE — Effectively total loss. Roughly 99% mortality within 8-10 years of infestation — not most of the ash, all of it.
YEAR 9: ~3% OF ASH STILL ALIVE — Effectively total loss. Roughly 99% mortality within 8-10 years of infestation — not most of the ash, all of it.
YEAR 10: ~1% OF ASH STILL ALIVE — Effectively total loss. Roughly 99% mortality within 8-10 years of infestation — not most of the ash, all of it.

How the beetle actually kills a tree

The adult lays eggs on the bark. Larvae hatch and tunnel into the layer just underneath, chewing S-shaped galleries through the tissue the tree uses to move water and sugar. Enough of those and the tree is girdled from the inside. It starves.

What decline looks like

Ash decline starts at the top. Leaves stop coming out on the upper branches, and the dieback works downward year over year. Meanwhile the trunk often throws out a mess of frantic new shoots down low. That is the tree panicking, not recovering.

One local exception worth knowing about

Five native ash species get attacked here. Four of them are highly susceptible. Blue ash is the odd one out. It holds up noticeably better than the rest, and it is an uncommon tree that happens to grow in southwestern Ontario.

Essex County is one of the few places in Canada where you might actually have one. It is not immunity, but a blue ash still standing with a full crown in 2026 is a genuinely different situation from a green or white ash in the same condition. Worth having someone identify which you have before you decide anything. Our arborist services in Windsor cover species identification.

INTERACTIVE — SUSCEPTIBILITY BY NATIVE ASH SPECIES
GREEN ASH
WHITE ASH
BLACK ASH
PUMPKIN ASH
BLUE ASH
GREEN ASH — ~99% MORTALITY — The most common ash in Windsor-Essex yards and fence lines — and among the first to die. Highly susceptible.
WHITE ASH — ~97% MORTALITY — The big woodlot ash. Highly susceptible; large specimens lasted only a few seasons longer than green ash.
BLACK ASH — ~99% MORTALITY — Wetland species, culturally significant for basketry. Highly susceptible and now at risk across its range.
PUMPKIN ASH — ~98% MORTALITY — Rare Carolinian species at the northern edge of its range here. Highly susceptible.
BLUE ASH — ~35% MORTALITY — The local exception. Holds up noticeably better — and Essex County is one of the few places in Canada you might actually have one. Worth identifying before any removal decision.

If you still have an ash tree in Windsor-Essex

Be careful about what you are looking at. Twenty-four years past ground zero, a standing ash here is almost never a healthy tree that has not been found yet. It is usually a dead or dying tree that has not come down yet.

That distinction matters more than people expect, because dead ash does not behave like other deadwood. It goes brittle fast. Limbs snap off with no warning and no bend to them. Climbers will not tie into a long-dead ash, which is why these removals often need a bucket or a crane, and cost more than an equivalent live maple would.

We have had homeowners in South Windsor and Tecumseh call in October about a tree they had been keeping an eye on since spring, after a limb went through a fence. The tree was unclimbable by then. Waiting made the job bigger and more expensive, not cheaper.

Get the tree looked at

If you have an ash on your property, or something you think might be an ash, have somebody put eyes on it before the next windstorm decides for you.

Tree Removal Windsor takes down dead and declining ash across the county. We work in tight backyards without tearing up the lawn, we carry full liability insurance and WSIB clearance, and we will tell you straight whether a tree needs to come down.

We also cover LaSalle, Tecumseh, Amherstburg, Leamington, Kingsville, and Essex.

Assessments are free and you get the number in writing. Request a quote.