Two systemic insecticides have proven highly effective at protecting ash trees from emerald ash borer (EAB): emamectin benzoate, delivered by trunk injection, and imidacloprid, applied as a soil drench or trunk injection. Emamectin benzoate is the stronger performer, providing up to three years of protection from a single treatment. Which product you choose, and whether treatment makes financial sense at all, depends on your tree’s size, its current health, and how long you plan to keep protecting it.
How Emerald Ash Borer Kills Trees
EAB is a beetle native to Asia that feeds on the inner bark of ash trees during its larval stage. The larvae chew S-shaped tunnels, called galleries, through the tissue that moves water and nutrients between roots and canopy. Once enough of that tissue is destroyed, the tree starves. A heavily infested ash can go from healthy-looking to dead in two to four years. The pest threatens at least 16 North American ash species and has already killed hundreds of millions of trees across the continent.1Oxford Academic (Journal of Economic Entomology). Laboratory Evaluation of the Toxicity of Systemic Insecticides to Emerald Ash Borer Larvae
Because the larvae feed beneath the bark where contact sprays cannot reach them, effective treatment requires systemic insecticides that the tree absorbs and distributes through its vascular system. The chemical ends up in the tissues the larvae are eating, killing them before they can do serious damage. This is the principle behind every treatment discussed below.
Emamectin Benzoate Trunk Injection
Emamectin benzoate, sold commercially as TREE-äge, is the most effective chemical treatment available for EAB. It is injected directly into the trunk through small ports drilled into the base of the tree. The insecticide moves upward through the sapwood and accumulates in the canopy, where it kills larvae feeding in the bark and adults feeding on leaves.
Field research has consistently shown outstanding results. In a multi-year study, a single trunk injection provided complete control of EAB larvae in 98 out of 99 treated trees, and that protection lasted two to three years depending on the dose.2Arboriculture & Urban Forestry. Multiple-year Protection of Ash Trees from Emerald Ash Borer with a Single Trunk Injection of Emamectin Benzoate, and Single-year Protection with an Imidacloprid Basal Drench That is a remarkable success rate for a pest this destructive. Beyond just keeping larvae at bay, treated trees showed measurable improvements in chlorophyll concentration and overall plant fitness over the course of treatment, with peak improvement occurring in the second year. Untreated control trees, by contrast, continued declining every year of the study.3Arboriculture & Urban Forestry. Physiological Response of Ash Trees, Fraxinus spp., Infested with Emerald Ash Borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), to Emamectin Benzoate (Tree-Äge) Stem Injections
The injection hardware matters. Research comparing different injection systems found that while all systems provided excellent protection for the first two years, only those using a higher number of injection ports (specifically, 16-port systems) extended protection out to three years.4Arboriculture & Urban Forestry. Factors Affecting Efficacy of Trunk-Injected Emamectin Benzoate to Manage Emerald Ash Borer More ports mean the insecticide distributes more evenly through the tree, covering a greater proportion of the vascular tissue. If your arborist offers a choice, a system with more injection points is generally worth it for the longer protection window.
One practical drawback: emamectin benzoate injections typically require a licensed applicator. The equipment and product are professional-grade, and in most states you need a pesticide applicator license to purchase and use TREE-äge. Budget roughly $100 to $250 per treatment depending on tree size and your local market, though this can vary widely.
Soil-Applied Imidacloprid
Imidacloprid is a neonicotinoid insecticide that can be applied as a soil drench around the base of the tree. The roots absorb it, and it moves upward into the canopy. This is the treatment most accessible to homeowners, since products like Bayer Advanced Tree and Shrub Insect Control are available at garden centers without a professional license.
Imidacloprid works, but with an important limitation: tree size matters a lot. Annual soil drenches provided complete protection of smaller ash trees (those with trunk diameters under about 30 centimeters, or roughly 12 inches) for three years of treatment. However, most of the larger trees in the study, those with trunk diameters above 38 centimeters (about 15 inches), declined to a weakened and visually poor condition despite treatment.5PubMed. Protection of individual ash trees from emerald ash borer (Coleoptera: Buprestidae) with basal soil applications of imidacloprid The reason is straightforward: as a tree’s trunk diameter doubles, the surface area of trunk and branches increases roughly fivefold, so the same dose of insecticide has to spread across much more tissue.
Application rate and timing also affect results. Research comparing different neonicotinoids found that spring applications of imidacloprid worked better than fall applications, and that higher application rates provided more consistent protection.6PubMed. Efficacy of Soil-Applied Neonicotinoid Insecticides for Long-term Protection Against Emerald Ash Borer (Coleoptera: Buprestidae) If you are going the homeowner route with a soil drench, applying in mid-spring when the tree is actively taking up water gives the insecticide the best chance of reaching the canopy before peak beetle activity in early summer.
For large, high-value ash trees, most extension services now recommend emamectin benzoate trunk injection over soil-applied imidacloprid. The trunk injection puts the insecticide directly into the vascular system regardless of tree size, bypassing the uptake bottleneck that limits soil drenches on big trees.
Azadirachtin as a Botanical Alternative
If you want to avoid synthetic insecticides, azadirachtin is a plant-derived option worth knowing about. It comes from neem tree seeds and works as an insect growth regulator, disrupting larval development rather than acting as a traditional nerve poison. Research has shown that trunk injections of azadirachtin inhibit EAB larval development, reduce adult emergence, and produce foliar residues at concentrations high enough to be biologically effective.7PubMed. Azadirachtin: an effective systemic insecticide for control of Agrilus planipennis (Coleoptera: Buprestidae)
Follow-up work on both white and green ash confirmed that azadirachtin residues in foliage remained above the thresholds needed to affect both larval and adult EAB life stages for a useful period after injection.8Pest Management Science. Foliar residue dynamics of azadirachtins following direct stem injection into white and green ash trees for control of emerald ash borer Researchers have specifically noted its potential as an environmentally acceptable option for protecting high-value urban ash trees.
The tradeoff is that azadirachtin has not been tested as extensively as emamectin benzoate, and its track record in long-term field trials is thinner. It also typically requires annual injection rather than the two-to-three-year intervals possible with emamectin benzoate. For someone managing a single yard tree and prioritizing lower environmental impact, it is a credible option. For a municipality protecting hundreds of street trees, the logistics of annual injection for every tree usually tip the decision toward emamectin benzoate.
Does Tree Species or Drought Change How Well Treatment Works?
A common worry is that drought stress or differences between ash species might prevent the tree from distributing the insecticide properly. Research tracking radiolabeled imidacloprid through trunk-injected green ash and white ash trees found that insecticide concentrations did not differ significantly between the two species or between well-watered and drought-stressed trees. Beetle mortality was similar across all groups in both years of the study.9Elsevier / Crop Protection. Distribution of trunk-injected 14C-imidacloprid in ash trees and effects on emerald ash borer (Coleoptera: Buprestidae) adults
This is reassuring, especially during dry summers when you might wonder whether your treated tree is still protected. Trunk injection appears to work regardless of the tree’s water status, at least for imidacloprid. The caveat is that this study was conducted under controlled conditions; a tree that is severely drought-stressed and already losing canopy from dehydration faces compounding problems that no insecticide can fully address.
When Should You Decide Not to Treat?
Not every ash tree is a good candidate for treatment. The general guideline from university extension programs is that a tree should still retain at least half of its canopy before treatment is likely to save it. Once an ash has lost more than half its crown to EAB damage, the internal tissue destruction is usually too extensive for an insecticide to reverse. At that point, removal is often the safer and more practical choice, since a heavily damaged tree becomes a hazard as dead branches shed.
Tree location and personal value also matter. A large ash shading your house or anchoring your backyard is a very different proposition from a small ash at the back of a woodlot. Treatment costs accumulate over years, and you are committing to an indefinite schedule for as long as EAB remains active in your region. For a tree that is structurally sound, well-located, and still reasonably healthy, treatment almost always makes sense. For a tree that is already compromised, leaning, or in a spot where its loss would be inconsequential, the math shifts quickly toward removal and replanting with a non-ash species.
The Economics of Long-Term Treatment
One of the most practical questions homeowners and municipalities face is whether ongoing treatment costs less than removing the tree and replacing it. A bioeconomic analysis comparing different management strategies found that, besides simply removing all ash trees, the least expensive option over the long term was committing to injection in perpetuity. The study also found that the “remove only” strategy was the only scenario in which cumulative costs exceeded the appraised value of the trees, resulting in a net financial loss.10Oxford Academic (Journal of Economic Entomology). A bioeconomic analysis of objective-based management options for late-stage emerald ash borer (Coleoptera: Buprestidae) infestations
In plain terms: removing all your ash trees is the most expensive thing you can do. Treating them indefinitely is cheaper than removal when you factor in the value the mature trees provide, including shade, property value, stormwater management, and aesthetics. This finding applies most strongly to large, healthy trees whose appraised value is high. For smaller or already-declining trees, the break-even calculation favors removal sooner. The key insight is that many homeowners default to “I’ll deal with it when the tree dies,” but by then the removal cost is at its highest (dead ash trees are brittle and more dangerous to take down) and the tree’s value is gone.
Biological Control and the Slow Cavalry
While chemical treatment protects individual trees, researchers have also been releasing parasitoid wasps from Asia that attack EAB larvae in their galleries. These tiny wasps lay their eggs on or near EAB larvae, and the wasp offspring consume the beetle larvae as they develop. The USDA has released several species across the eastern United States since the mid-2000s, and there is growing evidence that they are establishing and spreading on their own.
Recent field work in central Kentucky found that about a third of EAB larvae were parasitized, even though the nearest deliberate parasitoid releases had occurred over 20 kilometers away and seven years earlier. Two introduced species, Tetrastichus planipennisi and Spathius galinae, accounted for most of the parasitism, alongside a native parasitoid. The Kentucky finding represented the farthest south that S. galinae had established in the United States at the time of the study.11Oxford Academic (Journal of Economic Entomology). Influence of anthranilic diamide insecticides on emerald ash borer (Coleoptera: Buprestidae) larvae and establishment of introduced parasitoids in central Kentucky
Biological control will not save your backyard ash tree this year. The parasitism rates, while encouraging, are nowhere near high enough to prevent tree death on their own. But over decades, as parasitoid populations build, they could reduce EAB pressure enough that some ash trees survive without chemical intervention. This is the long game, and it is the primary strategy for wild forest ash trees that nobody is going to inject individually.
Preventing Spread Through Firewood
One of the most effective things you can do at a community level has nothing to do with insecticides. EAB larvae travel inside ash firewood, and moving firewood from infested areas to clean ones is one of the main ways the beetle jumps to new regions. Modeling research has shown that restricting firewood transport, even imperfectly, can dramatically slow the spread of infestations between areas.12PubMed Central. Modelling Interactions between Forest Pest Invasions and Human Decisions Regarding Firewood Transport Restrictions
The models show that making locally sourced firewood cheaper and more convenient than transported firewood is one of the most powerful levers. Even modest changes in the relative cost of local versus transported wood cause large shifts in behavior that can prevent or delay an infestation from reaching new patches.13PubMed Central. Coupled Human-Environment Dynamics of Forest Pest Spread and Control in a Multi-Patch, Stochastic Setting The practical takeaway: buy firewood where you burn it, and do not bring ash firewood home from a camping trip. Many states have quarantine regulations that make transporting untreated ash wood across county or state lines illegal.
Breeding Ash Trees That Can Fight Back
The ultimate solution to EAB would be ash trees that resist the beetle on their own, much as some Asian ash species do in the beetle’s native range. Researchers are working on this, but it is early-stage science. One line of work uses a tissue-culture technique called somatic embryogenesis to clone ash trees that show signs of natural resistance, allowing mass propagation of promising genetic lines.14Springer Nature. Application of somatic embryogenesis for development of emerald ash borer-resistant white ash and green ash varietals Researchers have successfully induced embryogenesis in white ash, though induction rates vary depending on the timing of seed collection and the growth regulators used.
Scattered “lingering ash” trees that survive in heavily infested forests without treatment are another source of hope. These survivors may carry heritable resistance traits that breeders can select for. Identifying and propagating them is an active area of research, but turning a handful of survivor trees into a commercially available resistant variety takes decades of breeding, testing, and nursery production. For the foreseeable future, if you want to keep a specific ash tree alive, chemical treatment remains the only reliable option.