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Trunk injection puts treatment inside the tree instead of on top of it. A small port is drilled at the base, the material is metered directly into the vascular system, and the tree distributes it through the canopy on its own. Nothing is sprayed into the air, nothing runs off onto the ground, and neighboring plants are not exposed. For borers already tunnelling under the bark, and for vascular diseases moving inside the wood, it is often the only delivery method that actually reaches the target.
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Injection is a delivery method, not a single product. What goes in depends entirely on what the inspection finds.
Insects that spend their life cycle under the bark are almost untouchable from the outside. A systemic insecticide injected into the trunk moves with the tree’s own water column into the tissue those larvae are feeding on. This is the standard approach for bronze birch borer and for ash at risk from emerald ash borer.
Aphids and adelgids on large conifers sit far above the reach of any ground-based sprayer. Injection treats a 70-foot spruce from the base, and one application generally carries through multiple seasons rather than needing repeat visits.
Some pathogens travel inside the water-conducting tissue where a foliar spray never lands. Injected fungicide is used preventatively on high-value elms and on ornamentals with a repeating anthracnose history.
Phosphite treatments are used to support trees under root-disease pressure, particularly on sites with poor drainage. These are a preventative and suppressive tool — they do not eliminate an established root pathogen, and we will say so plainly rather than sell a cure.
These are the conditions our arborists are asked about most often across Auburn, Kent, Federal Way, Renton, Tacoma and Puyallup, and where injection has a genuine advantage over other delivery methods.
| Tree | Problem | Why injection is the right delivery |
|---|---|---|
| Birch | Bronze birch borer (Agrilus anxius) — native to the region and a persistent killer of stressed ornamental birch | Larvae feed under the bark; nothing applied to the outside of the tree reaches them |
| Ash | Emerald ash borer (Agrilus planipennis) — confirmed in Washington for the first time in 2026 near Vancouver, and active in Oregon since 2022 | Systemic injection is the only established protective treatment for a standing ash |
| Spruce | Spruce aphid (Elatobium abietinum) and Cooley spruce gall adelgid (Adelges cooleyi) | Canopy height on mature spruce puts the infestation out of spray range from the ground |
| Douglas fir | Douglas-fir beetle (Dendroctonus pseudotsugae) — a native bark beetle that moves into stressed and declining Douglas fir | Injection is highly effective against it; the beetle feeds and breeds under the bark, out of reach of anything applied to the outside, so the treatment has to already be in the tree |
| Pine | Western pine beetle (Dendroctonus brevicomis) | Attacks kill quickly once they succeed, so the treatment has to be in the tree beforehand; a single injection can carry a pine through several seasons |
| Elm | Dutch elm disease (Ophiostoma novo-ulmi) — detected in Washington in Spokane, Tacoma and Bellevue | A vascular pathogen has to be met inside the vascular system |
| Maple, dogwood, sycamore | Repeating anthracnose and Verticillium wilt (Verticillium dahliae) pressure | Reaches infection sites that a canopy spray cannot cover on a large tree |
Not every tree on this list is a candidate. Advanced decline, extensive canopy loss, or structural failure can put a tree past the point where treatment is worth the money — we will tell you that instead of injecting it.
An ISA Certified Arborist walks the property, identifies the species, and inspects for the specific damage pattern rather than guessing from symptoms alone.
We confirm what is causing the decline. If the problem is drainage, compaction, root damage or previous poor pruning, injecting the tree will not fix it.
You get the target pest or pathogen in writing, the treatment interval, and the cost, with no obligation.
A licensed applicator performs the injection. Because the material goes inside the trunk rather than into the air, there is no spray drift onto adjacent plantings or property.
We re-inspect on the interval the treatment calls for and adjust the plan based on what the tree does, not on a fixed sales schedule.
Most single-tree injections are finished inside 30 to 60 minutes once the arborist is set up. Larger trees and multi-tree properties take longer, but injection is a same-visit treatment — there is no need for you to be home and no need to keep anyone off the property afterward.
It depends on the material and the target. Some systemic insecticide treatments carry protection for multiple growing seasons from a single application, while fungicide and phosphite programs are set on a shorter interval. We put the interval in writing with the quote so you are not guessing when the next visit is due.
The injection port is small and shallow and the tree compartmentalises it the same way it responds to any minor wound. Modern injection equipment is designed to minimise the wound and the number of ports required. The alternative — leaving an active borer infestation untreated — does far more damage than the port ever will.
For anything living under the bark or inside the vascular system, yes, because a spray physically cannot reach it. For surface-feeding insects, leaf pathogens and fruit tree programs a foliar application is often the better fit. They are different tools and we pick based on the diagnosis — see tree spraying for the other side of that.
Yes. Emerald ash borer was recorded in Washington for the first time this year, near Vancouver, after being active in Oregon since 2022, and it is continuing to spread rapidly. It has not been reported in King or Pierce County yet, but waiting for it to show up is the wrong plan — an ash is treatable while its canopy is still full, and a far poorer candidate once dieback starts at the top. If you have a mature ash you intend to keep, the right move is preemptive treatment now, kept up on a repeating schedule. Our arborists confirm the species, assess the tree, and tell you whether it is worth treating.
We will tell you. If the canopy loss, decay or root damage has gone past the point where treatment changes the outcome, spending money on injection is not in your interest. In that case we quote removal, or write an arborist report if a city or an insurer needs the condition documented.
Treatment is quoted per tree after an on-site inspection — species, trunk diameter, the number of trees, and access all change the number. The consultation and the written quote are free.
Injection is priced by trunk diameter, application rate, and solution. In cases where a tree is too far gone to justify treatment we will say so and price the alternative instead — see tree removal or ask for an arborist report if you need the condition documented.
Every certification number below links to that arborist’s credential record with the International Society of Arboriculture, so you can verify it before anyone sets foot on your property.
Washington L&I Contractor License PACIFA*813KG · WSDA Pesticide Applicator #109480 · $1M liability insured
Send us the tree and what you are seeing and one of our ISA Certified Arborists will come out - free of cost, to diagnose it, and give you a written quote. Photos help — you can attach them to the form.
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