Pest and disease treatment
Diagnosing and treating insects and diseases, like emerald ash borer, spongy moth and fungal problems.
What it is
A pest and disease specialist first figures out what's actually wrong. Many problems that look alarming are cosmetic and harmless. When treatment makes sense, options include trunk injections (for example, TreeAzin for emerald ash borer), targeted sprays, pruning out infected wood, and improving the tree's growing conditions.
Ontario bans cosmetic pesticide use. Homeowners may only use low-risk products from the provincial allowable list. Stronger treatments for tree health need a written opinion from a qualified arborist or forester, a licensed applicator, and advance notice to neighbours.
Signs you might need it
- Thinning canopy, dieback from the top, or D-shaped exit holes in ash bark
- Leaves chewed down to the veins in early summer (possibly spongy moth)
- Leaves wilting and turning yellow or brown in mid-summer
- Sap oozing, cankers or mushrooms on the trunk
- Caterpillar nests or egg masses on the bark
Good to know
Treatment works best early. A tree that's more than about 30–50% dead is usually not worth treating and may need removal instead.
Typical cost in Ontario
Before HST. Injections are priced by trunk width (one Toronto company charges about $10 per inch) and must be repeated every 2 years while emerald ash borer is in the area. Other treatments are quoted per job.
What pushes the price up or down
- Trunk width (the biggest factor for injections)
- Product and method: injection, spray or soil treatment
- How often it must be repeated
- How far the infestation has spread
- Number of trees treated in one visit
Ways to spend less
- Treat healthy ash trees early; a badly infested tree often needs removal anyway
- Treat several trees in one visit, and get the per-inch rate and re-treatment schedule in writing
- For small, reachable trees, allowed low-risk products (like Btk for spongy moth caterpillars) and scraping off egg masses can help
Only one current Ontario company publishes an injection rate. Ontario pesticide rules come from ontario.ca. Prices are typical ranges gathered from published Ontario price guides and company price pages in September 2026, before 13% HST. They’re a guide, not a quote: your price depends on your tree and your property. Get two or three written quotes, and check whether your city charges a permit fee.
Find a company for this work
Search the directory by your town, then filter by specialization. Every company is ranked by ARB Score, and no company can pay for a higher position.
Related specializations
Sources for the prices on this page
- Using pesticides in Ontario – Government of Ontario (Ontario)
- Pesticides Act – Ontario Regulation 63/09 (General), text via FAOLEX (original 2009 text; check current e-Laws for amendments) (Ontario)
- Important Things to Know About Tree Pesticides in Ontario - Five Star Tree Services (Ontario)
- Tree Service Prices in Toronto & GTA | Local Arborist (Toronto / GTA, ON)
- Insecticide could exterminate Fredericton's emerald ash borer population, expert says | CBC News (New Brunswick, Canada)
- Emerald Ash Borer Treatment - Forestar (Rockwood / Guelph, ON)
- Emerald Ash Borer (EAB) and Ash Tree Injections - City of Toronto (Toronto, ON)
- Spongy Moth – City of Toronto (Toronto, ON)
- Emerald Ash Borer Disease Management in Ontario - Arborcorp (Oakville / Halton, ON)
- Emerald Ash Borer – Town of Oakville (Oakville, ON)
- How Much Does an Arborist Cost? (2026) – HomeGuide (US prices, in US dollars)
- How Much Does an Arborist Cost? – Angi (US prices, in US dollars)