Emerald Ash Borer in Guildwood: What Scarborough Homeowners Need to Know Before It's Too Late

Guildwood was built around its trees.

When Rosa and Spencer Clark developed the neighbourhood in 1957, they enshrined a founding principle in the community's design: preserve the existing forest wherever possible. The result is one of Scarborough's most extraordinary neighbourhoods — winding streets, underground utilities, and mature canopy trees that tower over nearly every lot.

Those same trees, now 65–70 years old, are the neighbourhood's greatest asset. They are also, right now, its most urgent liability.

The Emerald Ash Borer has arrived in Guildwood — and if you have an ash tree on your property, you need to act.

What Is the Emerald Ash Borer?

The Emerald Ash Borer (Agrilus planipennis) is a metallic green beetle native to Asia. It was first detected in North America in 2002 and reached Toronto in 2007. In the nearly two decades since, it has killed more than 800,000 ash trees across the city — a figure confirmed by the City of Toronto's Urban Forestry division.

In Scarborough alone, estimates put the number of dead or dying ash trees at 100,000+.

EAB is not like most tree pests. It kills efficiently, it spreads fast, and by the time visible symptoms appear on the outside of the tree, the damage underneath is often already severe. The beetle attacks all species of true ash (Fraxinus sp.) — white ash and green ash, the two most common mature ash species on Guildwood lots, are both primary targets.

The City of Toronto treats select City-owned boulevard trees with TreeAzin injections. Private property trees are entirely the homeowner's responsibility. The City does not fund or perform treatment on trees in your yard.

Why Guildwood Is Especially Vulnerable

Most ash trees in Guildwood were planted in the late 1950s and 1960s — they are now among the largest, most mature specimens in east Toronto. Large, old trees are both more valuable and more dangerous when they die.

A dead ash tree loses structural integrity quickly. Within 2–3 years of death, the wood becomes extremely brittle — unpredictable under chainsaw cuts, prone to sudden branch failures, and hazardous for any arborist who tries to climb it. Crane-assisted removal is frequently the only safe option for dead ash in Guildwood, which adds to the cost and complexity.

The neighbourhood's original design, which we now celebrate for its beauty, also means that many of these large trees are sandwiched between homes, in tight lots, or hanging over fences and driveways. There is no margin for error.

How to Tell If Your Ash Tree Is Infested

EAB often kills from the inside out. By the time you notice anything is wrong, the infestation may already be advanced. Here are the signs to look for:

Early signs:

• Canopy thinning starting at the top of the tree and working downward
• Increased woodpecker activity — birds excavate bark to reach the larvae beneath

Clear infestation signs:

• D-shaped exit holes in the bark, about the size of a pencil eraser — this is the definitive sign of adult beetles emerging
• S-shaped larval galleries visible when bark is peeled back (the feeding tunnels left by larvae)
• Epicormic shoots — clusters of new growth sprouting directly from the trunk or major branches, a stress response to the canopy being killed from above

Late-stage / critical signs:

• More than 50% of the canopy appears dead or has failed
• Major branch dieback throughout the crown
• Bark cracking and falling away from the trunk

If you see D-shaped holes or S-shaped galleries, the tree is confirmed infested. Call an ISA Certified arborist immediately to assess how far the damage has progressed.

Treatment vs. Removal: How to Decide

Here is the decision that every Guildwood homeowner with an ash tree needs to make.

TreeAzin Injection — When It Can Save Your Tree

If your ash tree has lost less than approximately 30–50% of its canopy, it may still be a candidate for treatment with TreeAzin — a biopesticide derived from neem tree seeds that is injected directly into the trunk. TreeAzin kills EAB larvae feeding under the bark and deters adult beetles from laying eggs on the treated tree.

Key facts about TreeAzin treatment:

• Cost: approximately $200–$600 per treatment, depending on trunk diameter (some providers charge ~$8 per centimetre of diameter)
• Frequency: treatment must be repeated every 2 years to maintain protection
• Effectiveness: good results when the tree is caught early enough; treatment is ineffective on trees past the recovery threshold
• Who can apply it: a licensed pesticide applicator, typically an ISA Certified arborist

TreeAzin is the only viable treatment for EAB on private property. It will not cure a tree that is already past recovery, and it does not eliminate EAB from the area — it only protects the individual tree.

The City of Toronto treats its own boulevard trees on a 3-year injection rotation starting in 2025. This program does not extend to trees on private property.

Removal — When It Is the Only Safe Option

If your ash tree has lost more than 50% of its canopy, treatment is unlikely to save it. At that point, removal is not just the responsible choice — it is urgent.

Dead ash trees present three problems that get worse every year they are left standing:

1. Brittleness: Dead ash wood desiccates rapidly, becoming fragile and unpredictable. Branches can fail without warning. A tree that looked manageable two years ago may now require crane-assisted removal because no one can safely climb it.

2. Liability: If a dead ash on your property falls and damages a neighbour's home or vehicle, you can be held liable — particularly if you knew the tree was dead and failed to address it. An ISA Certified arborist's written assessment documenting the hazard protects you.

3. Toronto permit requirements: You still need a permit to remove a dead ash tree in Guildwood if the trunk is 30 cm or more in diameter. Removing it without a permit — even an obviously dead hazard — exposes you to fines.

The Permit Reality in Guildwood

This is where Guildwood gets complicated, and where many homeowners make costly mistakes.

Chapter 813 — The Private Tree Bylaw

Under Chapter 813 of the Toronto Municipal Code, a permit is required to remove any tree on private property with a trunk diameter of 30 cm or more (measured at 1.4 m above ground level). Given that Guildwood's trees were planted 65+ years ago, nearly every mature specimen qualifies.

What the permit process involves:

• An arborist report documenting the tree's condition and justification for removal
• A site plan showing the tree location and adjacent trees
• A replanting or landscape plan — replacement planting is mandatory as a permit condition
• Application submitted to the Scarborough District Urban Forestry office, Scarborough Civic Centre, 150 Borough Drive, 3rd Floor
• City has up to 30 business days to review a complete application

The fine for removing a regulated tree without a permit is up to $100,000 per tree.

Chapter 658 — The Ravine Bylaw

Guildwood sits along the Scarborough Bluffs. Many properties south of Guildwood Parkway have backyards that fall partially or fully within a designated ravine or natural feature area under Chapter 658 — the Ravine and Natural Feature Protection Bylaw.

Unlike Chapter 813, which is size-based, Chapter 658 protects every tree regardless of size or species within the protected zone. Removing a small ash sapling in a Chapter 658 area requires the same authorization as removing a large mature tree.

If your property is affected by Chapter 658, you need a separate Ravine and Natural Feature Permit application, which requires the ravine line delineation to be shown on your site plan.

Not sure whether Chapter 658 applies to your property? Our arborists know how to check — and we handle the application either way.

What UTS Does for Guildwood Homeowners

We have been serving east Scarborough — including Guildwood — from our Ajax base for years. Here is exactly what we do on every Guildwood ash tree job:

1. Free on-site EAB assessment. We evaluate your tree, determine the percentage of canopy loss, look for D-shaped exit holes and larval galleries, and give you an honest recommendation — treatment or removal.

2. TreeAzin candidacy evaluation. If the tree qualifies for treatment, we advise you on the realistic probability of recovery and the ongoing cost of a 2-year injection program.

3. Toronto permit application preparation. For removal, we prepare the arborist report, site plan, and replanting plan. We submit to the Scarborough Civic Centre and follow up with the Scarborough District Urban Forestry office. You don't navigate this alone.

4. Removal using the right technique. For dead or advanced-infestation ash trees, we use crane-assisted or rigged sectional removal — the only safe approach for brittle wood in tight Guildwood lots. No shortcuts.

5. Cleanup and replanting advice. We leave the property clean and advise on replacement species appropriate for your lot and soil.

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The Bottom Line

If you have an ash tree in Guildwood, the question is not whether it is at risk. It is. The question is where it is in the infestation timeline — and whether you act before it crosses the point of no return.

Dead ash trees that could have been treated two or three years earlier are now crane jobs. Trees that were crane jobs two years ago are now safety emergencies. Every season you wait costs more and carries more risk.

Call us at (289) 200-8441 or get a free quote online. We will come to your Guildwood property, assess your ash trees honestly, and tell you exactly what they need — whether that's a $400 injection or a crane-assisted removal with a permit we file for you.

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Unparalleled Tree Service is ISA Certified, fully insured, and based in Ajax — 15 minutes from Guildwood via Kingston Road. See our full Guildwood service page or contact us with any questions.