You noticed something off — maybe the canopy is thinner than it was last summer, or there are small D-shaped holes in the bark you’ve never seen before. You searched around, found a few companies offering tree spraying service, and now you’re trying to figure out what that actually means and whether it will help.
Here’s the thing: “tree spraying” isn’t one treatment. It’s a category that covers three fundamentally different methods — foliar spray, bark spray, and trunk injection — and each one targets a different problem in a different way. Getting the right diagnosis and the right method is the difference between saving a tree and watching it decline for another season before it’s gone.
Three Methods of Tree Spraying Service — and What Each One Actually Does
Most homeowners assume treating a tree means spraying something on the outside of it. That’s sometimes true — but it’s only part of the picture. Foliar spray, bark spray, and trunk injection each work differently, reach different parts of the tree, and are suited to different threats. A company that recommends one without diagnosing the specific problem first isn’t giving you a treatment plan — they’re guessing.
Understanding the basics of each method helps you ask better questions, evaluate what you’re being told, and know whether the approach actually fits what’s happening to your tree.
Foliar Spray and Bark Spray: When Surface Application Makes Sense
Foliar spray is what most people picture: a product applied directly to the leaves, branches, or bark of a tree. It works well for surface-level pests — aphids, scale insects, spider mites — and for certain fungal diseases like anthracnose that affect leaves during wet spring weather.
In Oakland County, anthracnose is a recurring issue. Our springs tend to be wet, and that moisture creates ideal conditions for fungal spores to spread across the leaf surface. Foliar sprays applied at the right time in the season can interrupt that cycle before serious defoliation sets in.
Bark spray is a variation of surface application, typically used to target insects that live in or just beneath the outer bark layer. The product is applied to the trunk and main limbs rather than the canopy. It’s a useful tool for certain pest categories, but it has a real limitation: it can’t reach insects that have already burrowed deep into the tree’s tissue. If the pest is inside the tree, surface application — no matter how thoroughly applied — isn’t going to get there.
That’s an important point for Oakland County homeowners dealing with emerald ash borer. EAB larvae tunnel beneath the bark and feed on the cambium layer — the living tissue that moves water and nutrients through the tree. By the time you can see the D-shaped exit holes in the bark, the larvae have already been feeding under the surface for one to three years. A foliar spray applied to the outside of an infested ash tree won’t reach them. That’s where trunk injection becomes the right tool.
One other thing worth knowing about foliar spray: it loses product to drift, UV degradation, and runoff in ways that trunk injection doesn’t. That doesn’t make it the wrong choice for the right problem — but it does mean the method needs to match the target.
Trunk Injection: How It Works and Why It Reaches What Sprays Can’t
Trunk injection bypasses the surface entirely. Small ports are drilled into the base of the tree, and the treatment is delivered directly into the vascular system — the internal network the tree uses to move water and nutrients from the roots up through the canopy. From there, the tree’s own sap flow distributes the active ingredient throughout the entire tree, reaching the cambium layer, the inner bark, and the canopy from the inside out.
This matters enormously for pests like emerald ash borer, where the target is living beneath the bark and completely unreachable by surface application. It also matters for oak wilt, a lethal fungal disease that spreads through a tree’s vascular system and can kill a red oak within weeks of infection. Trunk injection with a fungicide called propiconazole is the primary treatment approach for oak wilt — and it works precisely because it’s delivered into the same system the disease uses to travel.
For EAB specifically, the most effective treatment available is emamectin benzoate trunk injection — sometimes marketed under the brand name TREE-äge. Research from Michigan State University and Ohio State University found that a single properly timed injection provided excellent control of emerald ash borer for at least two years, with evidence of protection extending to three years under favorable conditions. That’s not an annual commitment — it’s a long-duration treatment that gives a healthy or lightly infested ash tree a real chance at survival.
There’s a question we hear often: will the injection holes hurt the tree? The short answer is no. The ports are small, and research shows that treated trees rapidly begin producing new wood over the injection wounds in late summer following a spring treatment. The minor wound from an injection site is far less damaging than what an untreated EAB infestation does over the following two to three years.
Timing matters too. Trunk injection is most effective when the tree’s vascular system is actively moving — which means shortly after leaves have emerged in spring. In Michigan, the optimal window for EAB trunk injection is mid-May through early June. Applying outside that window reduces efficacy because the active ingredient can’t travel through the tree as effectively when sap flow is slow.
Emamectin Benzoate Tree Injection: What Oakland County Homeowners Need to Know
Emamectin benzoate is the strongest EAB treatment currently available — and it’s not something you can buy at a hardware store. It’s classified as a Restricted Use Pesticide under Michigan law, which means it can only be legally purchased and applied by a licensed pesticide applicator. That’s not a technicality — it’s a meaningful distinction between a professional treatment and whatever over-the-counter alternatives a homeowner might try on their own.
Oakland County’s ash trees have faced EAB pressure longer than almost anywhere else in the country. The original U.S. discovery of emerald ash borer happened in the Detroit metro area in 2002, and the pest has been working through Southeast Michigan’s ash population ever since. If you have a surviving ash tree on your property, the question isn’t whether EAB is present in your area — it is. The question is whether treatment is still viable.
Is It Too Late to Treat Your Ash Tree for Emerald Ash Borer?
This is the question that matters most for homeowners who’ve already noticed decline. The honest answer is that it depends on how far along the infestation is — and there’s a threshold worth knowing about.
Emamectin benzoate trunk injection works best as a rescue treatment when canopy decline is still limited — generally under roughly 50% canopy loss. Below that threshold, the tree’s vascular system is still functional enough to distribute the injected insecticide from the trunk out through the canopy. Above it, the internal damage may be too extensive for the treatment to move effectively, and the likelihood of recovery drops significantly.
EAB is particularly deceptive because the larvae can be actively feeding inside a tree for one to three years before visible symptoms appear on the outside. By the time you notice thinning canopy, yellowing leaves, or the characteristic D-shaped exit holes in the bark, the infestation may already be well established. That’s not a reason to panic — but it is a reason not to wait another season to have the tree assessed.
For homeowners in Farmington Hills, MI, Waterford, MI, Clarkston, MI, or any of the heavily wooded communities throughout Oakland County, the stakes are real. Many of the ash trees that were planted along residential streets and in subdivision lots in the 1970s and 1980s are now mature, established trees that would cost thousands of dollars to remove and are essentially irreplaceable in terms of the canopy they provide. A properly timed emamectin benzoate injection — applied by a licensed professional in May or early June — can protect that tree for two to three years per treatment cycle.
What you want to avoid is the “wait and see” approach. It’s the most common mistake we see, and it’s understandable — nobody wants to spend money on a tree that might recover on its own. But EAB doesn’t resolve on its own. And once a tree crosses the point where treatment is no longer viable, the only remaining option is removal.
Why the Company You Hire for Tree Spraying Service in Oakland County Matters
Not every company that offers tree spraying service in Oakland County is licensed to apply the treatments that actually work. Emamectin benzoate is a Restricted Use Pesticide — applying it without a Michigan MDARD Pesticide Application Business License is illegal. Homeowners who hire an unlicensed applicator have no legal recourse if the treatment fails or causes damage, and they may not even be receiving the product they think they’re getting.
Beyond licensing, the quality of the diagnosis matters. The right treatment method depends entirely on correctly identifying the pest or disease first. A company that shows up and recommends a spray without examining the tree, discussing its history, or explaining what they found isn’t diagnosing — they’re guessing.
We’re fully licensed and insured — carrying full general liability, workers’ compensation, and all required Michigan licenses and municipal registrations. Ivan is personally on-site for every job, which means the person assessing your tree is the same person overseeing the treatment. We also hold line-clearance certification meeting DTE and Consumers Energy standards, a specialized credential that goes well beyond standard tree care licensing.
We offer free on-site estimates with no obligation. If you’ve noticed signs of decline — thinning canopy, discolored leaves, holes in bark, branch dieback — the best first step is having someone look at the tree and tell you honestly what’s happening and what the options are. That conversation costs you nothing, and it gives you the information you need to make a real decision rather than a guess.
One more thing worth knowing: oak wilt is gaining momentum in Michigan, and it behaves very differently from EAB. Red oaks are highly susceptible and can die within weeks of infection. The fungus spreads through root grafts between neighboring trees and through sap-feeding beetles that are attracted to fresh pruning wounds. In Michigan, the no-prune window for oaks runs from April 15 through July 15 — pruning an oak during that window significantly increases the risk of infection. If you have mature oaks on your property in Troy, MI, Rochester Hills, MI, or anywhere else in Oakland County, this timing is worth knowing before you schedule any work.
Getting the Right Tree Spraying Service in Oakland County, MI
The method matters. Whether a tree needs foliar spray, bark spray, or trunk injection depends on what’s actually wrong with it — and that requires a real diagnosis, not a default recommendation. For the most serious threats in Oakland County right now, including emerald ash borer and oak wilt, trunk injection with the right product at the right time is often the difference between saving a tree and losing it.
If you’ve noticed something off with a tree on your property, don’t wait on it. The trees that are treatable today may not be treatable next spring. A free on-site estimate gives you a clear picture of what’s happening and what your options are — without any pressure to commit.
Ivan’s Tree Services serves Oakland County and the surrounding Southeast Michigan area. We answer the phone 24 hours a day, seven days a week, including holidays — so if you have a question or need someone to take a look, you don’t have to wait for a callback.