If you have an ash tree (Fraxinus species) in your Knoxville yard, you almost certainly have a problem. The Emerald Ash Borer (EAB, Agrilus planipennis) has been confirmed in Knox County since 2010, and according to the USDA Animal and Plant Health Inspection Service, mortality rates exceed 99% in untreated ash populations within 6-10 years of infestation. This is the most consequential tree-loss event in East Tennessee since the chestnut blight a century ago.
What Is Emerald Ash Borer?
EAB is a small, metallic-green beetle native to Asia. According to the Invasive Species Centre, adult beetles are about 1/2 inch long and emerge from infested trees from May through August. They lay eggs in bark crevices; the resulting larvae tunnel under the bark, where they feed on the tree's vascular tissue — the part of the tree that moves water and nutrients between roots and leaves.
It's the larval feeding that kills the tree. Once enough vascular tissue is destroyed, the tree literally starves to death from the top down.
The Timeline of EAB in Tennessee
Per the Tennessee Department of Agriculture's official EAB tracking:
- 2002: EAB first detected in Detroit, Michigan
- 2010: First Tennessee detection in Knox County
- 2017: Tennessee placed under federal EAB quarantine for the entire state
- 2021: USDA eliminated the federal quarantine — not because EAB was eradicated, but because the pest had become too widespread to contain
- 2026: EAB confirmed in all 95 Tennessee counties
The implication for Knoxville homeowners: if you have an untreated ash tree, it has almost certainly been exposed.
How to Identify Ash Trees
Many homeowners aren't sure if they actually have an ash tree. Key identification features:
- Opposite branching — branches grow directly across from each other (not alternating). This narrows it to ash, maple, dogwood, or buckeye.
- Compound leaves — each "leaf" is actually 5-9 leaflets along a central stem
- Diamond-pattern bark on mature trunks — distinct ridge-and-furrow pattern forming diamond shapes
- Single seed wings — paddle-shaped "helicopter" seeds that fall in fall (different from maple's double-wing seeds)
The USA National Phenology Network and UT Extension both maintain free identification guides. The EmeraldAshBorer.info site (run by Purdue, Michigan State, and USDA) has the best photo-based ash identification resource online.
Signs of EAB Infestation
According to NC State Extension, look for these in your Knoxville ash trees:
- Canopy dieback starting at the top — leaves thinning out at the crown first
- Epicormic shoots — clusters of new branches sprouting from the trunk (the tree's emergency response)
- Bark splits revealing S-shaped larval galleries underneath
- D-shaped exit holes in the bark (about 1/8 inch wide) — distinctive of EAB
- Increased woodpecker activity — woodpeckers feed on EAB larvae, so heavy bark damage is often a sign
By the time you see canopy dieback, the tree is typically 3-5 years into infestation and has lost more than 30-50% of its vascular system. Treatment is much less effective at this stage.
Treatment Options for Valuable Ash Trees
Treatment is possible but expensive and requires ongoing commitment. Per the North Central IPM Center's multi-state treatment guide, options include:
Soil Drench (Imidacloprid)
- Cost: $30-$80 per treatment (DIY)
- Frequency: Annual
- Effectiveness: Moderate — works best on smaller trees (under 47 inches circumference)
- Application: Pour around the root zone in spring
Trunk Injection (Emamectin Benzoate / TREE-äge)
- Cost: $150-$400 per treatment (professional only)
- Frequency: Every 2-3 years
- Effectiveness: Most effective — proven 99%+ protection in clinical trials
- Application: ISA Certified Arborist injects directly into vascular system
Bark Spray
- Cost: $50-$150 per treatment
- Frequency: Annual
- Effectiveness: Lower than trunk injection
When Removal Makes More Sense Than Treatment
For most Knoxville homeowners, removal is the practical choice. Calculate the math:
| Scenario | Recommendation |
|---|---|
| Tree is large, healthy, and adds significant property value | Treat (trunk injection every 2-3 years) |
| Tree shows 30%+ canopy dieback | Remove — past the point of recovery |
| Tree is near a house, power line, or other target | Remove proactively before it becomes hazardous |
| Tree is small and replaceable | Remove and plant a non-ash species |
| Tree is in rural open area, away from targets | Could leave to die naturally (provides wildlife habitat) |
Critical safety note: dead ash trees become extremely brittle and dangerous within 1-2 years of dying. Per USDA Forest Service research, EAB-killed ash trees fail unpredictably and are responsible for multiple worker injuries each year. Removal becomes more dangerous (and expensive) the longer you wait after the tree dies.
EAB Ash Removal Cost in Knoxville
| Tree Size | Healthy Tree Cost | Dead Tree Cost |
|---|---|---|
| Small (under 30 ft) | $300-$500 | $400-$700 |
| Medium (30-50 ft) | $500-$1,000 | $800-$1,500 |
| Large (50-70 ft) | $1,000-$1,800 | $1,500-$2,800 |
| Massive (70+ ft) | $1,800-$3,000 | $2,500-$4,500+ |
The premium for dead/dying trees reflects the increased risk to climbers and the need for crane work in many cases. Removing while still healthy saves you 25-50%.
Disposal Restrictions
The Tennessee Department of Agriculture's quarantine required specific disposal practices to prevent further spread, including not moving firewood off the property. While the federal quarantine has ended, best practice remains:
- Burn ash wood on-site or have a licensed tree service haul it
- Don't transport ash firewood more than 50 miles
- Don't sell or give away untreated ash firewood
The DontMoveFirewood.org campaign remains the authoritative voluntary guidance.
What to Plant Instead
If you're removing an ash, consider these native Tennessee replacements per UT Extension recommendations:
- Yellowwood (Cladrastis kentukea) — native, fragrant flowers
- American Hophornbeam (Ostrya virginiana) — similar size and shape to small ash
- Sugar Maple (Acer saccharum) — comparable shade and fall color
- White Oak (Quercus alba) — long-lived (200+ years) replacement for large ash
Get a Professional Ash Assessment
If you suspect EAB on your Knoxville property, call (865) 348-3063 for a free assessment. We can evaluate the tree, identify the species (it's often not ash — many homeowners misidentify), and recommend treatment or removal based on the specific situation.
Sources and Further Reading
- USDA APHIS — Emerald Ash Borer Program
- Tennessee Department of Agriculture — EAB Information
- EmeraldAshBorer.info (Purdue + Michigan State + USDA partnership)
- UT Extension
- Don't Move Firewood Campaign
Related Knoxville Tree Pros guides: 7 Signs Your Tree Is Dying · Hazardous Tree Assessment