Emerald Ash Borer in Bloomington: What Every Homeowner Needs to Know
Emerald ash borer — EAB for short — is a small metallic-green beetle from eastern Asia that has caused more tree destruction across North America than any other invasive insect in recorded history. It arrived in Monroe County in the late 2000s, and its impact on Bloomington's landscape has been severe. Ash trees that once lined streets in Elm Heights, shaded back yards in Bryan Park, and anchored the canopy in Prospect Hill neighborhoods are largely gone now. Statewide, Indiana has lost tens of millions of ash trees to this pest.
The beetle itself is only half an inch long. The damage comes from its larvae, which feed on the inner bark tissue that carries water and nutrients up the tree. Within a few years of infestation, that pathway is severed and the tree starves from the crown down. Understanding how EAB works — and what you can do about it — is one of the most important pieces of tree knowledge a Bloomington homeowner can have right now.
How to Identify an Ash Tree on Your Property
Before you can manage EAB, you need to know whether you actually have an ash tree. Ash trees have several distinctive features that make identification straightforward once you know what to look for.
The most reliable identifier is the leaf arrangement. Ash trees have compound leaves with 5 to 11 leaflets arranged in opposite pairs along a central stem, with a single leaflet at the tip. The leaflets have slightly toothed edges and a pointed tip. No other common Monroe County tree has this exact combination of opposite, compound leaves — it immediately rules out hickory, walnut, and most other species with compound leaves.
The bark on a mature ash tree forms a tight, interlocking diamond pattern of ridges and furrows — often described as a fishnet or herringbone texture. This pattern becomes more pronounced as the tree ages. On younger ash trees, the bark is lighter gray and smoother, developing the diamond pattern more clearly over time.
Ash trees also have opposite branching — branches emerge from the trunk in matched pairs directly across from each other. Very few trees follow this pattern. If you see opposite branching, a compound leaf structure, and diamond-patterned bark together, you almost certainly have an ash. If you are still uncertain, an ISA-certified arborist can confirm the species during a free estimate visit.
Signs of Emerald Ash Borer Infestation
EAB infestations are not always obvious in their early stages. The beetle spends most of its life cycle beneath the bark, where the larval feeding damage occurs invisibly. By the time the most dramatic symptoms appear, the infestation is usually well advanced. Knowing the full range of signs — from early to late — gives you the best chance of catching the problem in time.
The most definitive sign is the D-shaped exit hole. When adult beetles emerge in late May and June, they chew through the outer bark in a very distinctive shape: a small, flat-sided oval that looks like a capital letter D, roughly 1/8 inch across. These holes appear on the trunk and main branches and are unlike any exit hole produced by native bark beetles, which leave round holes. A single exit hole is enough to confirm EAB is present.
Beneath the bark, EAB larvae feed in S-shaped or serpentine galleries that wind through the inner bark layer. If you peel away a section of bark from a declining ash — or if woodpeckers have already done this for you — these winding channels are a clear sign of larval feeding. Woodpecker activity is itself a valuable symptom to notice: pileated and red-bellied woodpeckers actively hunt EAB larvae, and heavy scaling of bark from the upper trunk of an ash tree often reveals a significant infestation beneath.
At the canopy level, EAB infestation produces a characteristic pattern of dieback that starts at the top of the tree and works its way downward. The upper crown thins and dies back first, while lower branches remain alive longer. As the tree declines, you will often see epicormic sprouts — small, desperate clusters of new growth erupting from the trunk and major branches well below the dying crown. This is the tree attempting to push out new growth below the point where the vascular system has been disrupted. In Monroe County, any ash tree showing crown dieback combined with epicormic sprouting is almost certainly EAB-infested and past the early treatment window.
Treatment Options: What Works and When
The good news about EAB is that effective treatment options exist. The bad news is that timing matters enormously. A tree treated early in an infestation can be saved and protected for years with ongoing management. A tree that has already lost too much canopy cannot be rescued by any treatment available.
The most effective treatment for high-value ash trees is TREE-äge, a product containing the active ingredient emamectin benzoate. It is applied via direct trunk injection — small ports are drilled into the base of the trunk and the product is injected under pressure directly into the tree's vascular system. Trunk injection is precise, minimizes chemical exposure to the surrounding environment, and provides protection for two to three years per treatment cycle. TREE-äge has shown excellent efficacy rates in research trials and is the treatment of choice when maximum protection is needed.
Soil-applied systemic insecticides containing imidacloprid are another option, applied as a drench or injection around the base of the tree. The tree takes up the product through its roots, and it circulates through the vascular system. Soil applications are generally less expensive per treatment cycle than trunk injection but take longer to move into the canopy and may be less consistent in efficacy, particularly on large-diameter trees or in very dry soil conditions. They work best as a preventive treatment on trees not yet infested.
The critical threshold for treatment is canopy condition. Trees that have lost less than 30 to 40 percent of their canopy to EAB dieback are generally good treatment candidates. Beyond that level of canopy loss, the tree's vascular system is too compromised to effectively distribute the treatment, and the structural integrity of the tree itself becomes a growing concern. If you are looking at an ash with more than a third of its crown dead or dying, the conversation should shift to safe removal rather than treatment.
The Danger of Dead Ash Snags
An untreated ash tree that succumbs to EAB does not simply stop growing — it becomes a progressively more dangerous structure in your yard. Homeowners who delay removal of dead ash trees often do not realize how quickly the wood deteriorates or how unpredictable that deterioration makes the tree.
Ash wood is naturally brittle compared to oaks and maples even when healthy. In a dead ash, the wood begins to degrade rapidly from the outside in. Bark starts to slip and separate from the trunk, large sections of the outer bark fall away, and the underlying wood is exposed to moisture, freeze-thaw cycling, and wood decay fungi. Within two to three years of death, a formerly sound ash can become a genuinely unpredictable structure — one that can drop large limbs without any wind event or other obvious trigger.
Removing a dead ash is also technically different from removing a living tree of the same size. Living trees have predictable wood properties that experienced crews account for in their cutting sequences. Dead ash with slipping bark, internal decay, and brittle wood requires additional precaution and often different rigging techniques to maintain control of the material. This is one reason dead ash removal is priced appropriately — it is not the same job as removing a healthy tree. Every year a dead ash stands on a Bloomington property, the tree becomes harder to remove safely and the potential for an uncontrolled failure event grows. Most arborists in Monroe County consider a dead ash with proximity to structures or traffic areas an urgent removal regardless of how it looks from the street.
Should You Treat or Remove? A Decision Framework
Deciding whether to invest in EAB treatment or proceed with removal is not always straightforward. Several factors should inform that decision, and working through them honestly produces the right answer for your specific situation.
Start with canopy condition. Use the 30 to 40 percent threshold as a hard rule. If you cannot honestly say the tree still has 60 percent or more of a healthy canopy, removal is the right call regardless of other factors.
Next, consider the tree's location and value. A large, mature ash that provides significant shade to your home's south or west exposure has real economic value — cooling costs are measurably lower in well-shaded homes. An ash at the far edge of a lot with no structural contribution to the landscape is a different calculation. An ash overhanging your roofline or standing close to a vehicle parking area adds a liability dimension that tips the balance toward removal even at moderate canopy loss.
Then compare the actual costs. EAB trunk injection treatment typically runs in the range of several hundred dollars per treatment cycle, with retreatment every two to three years. Over ten years, that is a real financial commitment. Compare that to the one-time cost of removal and consider whether the remaining functional life of the tree justifies the ongoing treatment cost. For a large, healthy ash that you value highly and that is still in the early stages of exposure, treatment is often worth it. For a smaller ash in poor overall health, removal and replacement planting of a non-susceptible species is often the better long-term investment.
If you have ash trees on your Monroe County property and are uncertain which path makes sense, a professional assessment gives you the information you need to decide. Bloomington Tree Service Pros provides free evaluations throughout the Bloomington area. Call (812) 432-2013 to schedule a visit from our ISA-certified arborists.
Get a Professional EAB Assessment in Monroe County
Emerald ash borer management is one of the most time-sensitive decisions a Bloomington homeowner can make. A tree that is a strong treatment candidate today may cross the threshold into removal territory by next season. Acting on an informed assessment now gives you the most options and the best outcomes.
Bloomington Tree Service Pros has worked with Monroe County property owners through the full EAB crisis — from the earliest detections in the late 2000s through the widespread losses that followed. Our ISA-certified arborists can evaluate your ash trees, give you an honest assessment of their current condition, and recommend the right path forward based on the actual tree in front of us, not a formula.
We offer TREE-äge trunk injection programs for treatable ash trees and full removal and cleanup services for trees that have reached the removal threshold. Call us at (812) 432-2013 to schedule a free, no-obligation assessment for any ash tree on your property. The earlier you get an answer, the more choices you have.