Since its discovery in Minnesota in 2009, the emerald ash borer (EAB) has killed hundreds of thousands of ash trees across the Twin Cities metro, and the numbers keep climbing every year. If you own property in Minneapolis, St. Paul, or anywhere in Hennepin, Ramsey, or Anoka County, there is a good chance you have at least one ash tree on your lot. Knowing how to spot the early warning signs of EAB infestation can mean the difference between saving a tree with prompt treatment and dealing with a costly emergency removal after the tree becomes a safety hazard.
Why Emerald Ash Borer Matters So Much in the Twin Cities
Minnesota has more ash trees than any other state in the country, with an estimated 1 billion ash trees statewide. In the Minneapolis and St. Paul urban forest alone, ash species make up close to 20 to 40 percent of the boulevard and park tree canopy in many neighborhoods, according to Minnesota Department of Agriculture (MDA) and DNR survey data. That concentration makes our region especially vulnerable to widespread canopy loss once EAB establishes itself in an area.
EAB has now been confirmed in dozens of Minnesota counties, including all of Hennepin, Ramsey, and Anoka Counties. Once a tree is infested, it typically dies within 2 to 4 years if left untreated. The insect does not discriminate between healthy, mature shade trees and young saplings, and it can spread quickly through firewood movement, so even properties that have never had an ash problem before can become infested seemingly overnight.
What Emerald Ash Borer Actually Is
The emerald ash borer is a small, metallic green beetle native to Asia, about the size of a cooked grain of rice (roughly 8.5 mm long). Adult beetles feed on ash foliage but cause minimal damage themselves. The real destruction happens underneath the bark, where larvae tunnel through the tree’s vascular tissue, cutting off the flow of water and nutrients between the roots and canopy.
Because the early stages of infestation happen beneath the bark, many homeowners do not notice a problem until the tree is already significantly compromised. That is why learning to recognize the visible clues early is so important for anyone with ash trees in the Twin Cities.
Top Signs Your Ash Tree Has Emerald Ash Borer
1. Canopy Thinning and Dieback
One of the earliest visible signs is thinning in the upper canopy, often starting at the top third of the tree. Leaves may appear sparse, undersized, or yellowed even during the growing season. Over time, entire branches in the upper crown will die back while lower branches may still look relatively healthy, at least initially. Homeowners often mistake this for drought stress or normal aging, which delays treatment.
2. D-Shaped Exit Holes
When adult beetles emerge from beneath the bark in late May through July, they leave behind distinctively shaped exit holes. These holes are D-shaped (flat on one side, rounded on the other) and only about 1/8 inch wide, roughly the size of a capital letter D printed in a standard font. You will typically find these on the trunk and larger branches, and they are one of the most reliable confirmation signs of EAB presence.
3. Bark Splitting and S-Shaped Galleries
As larvae tunnel and feed, the tree often responds by producing callus tissue, which can cause the bark to split vertically. If you peel back the bark in these areas, you may find winding, S-shaped tunnels (called galleries) packed with fine sawdust-like frass. These serpentine galleries are a hallmark sign of EAB larval feeding and distinguish it from other borers that tend to tunnel in straighter lines.
4. Increased Woodpecker Activity
Woodpeckers, especially downy and hairy woodpeckers, feed heavily on EAB larvae. A sudden increase in woodpecker damage, often called “flecking,” where patches of bark are stripped away in irregular sections, is a strong indicator that larvae are present underneath. If you notice significantly more woodpecker holes on one particular ash tree than in previous years, it is worth a closer inspection.
5. Epicormic Sprouting
Stressed ash trees often respond to vascular damage by producing epicormic shoots, which are small clusters of leafy sprouts growing directly from the trunk or main branches, sometimes at the base of the tree. This is the tree’s last-ditch effort to produce enough foliage to survive, and it is a sign that the internal damage is already fairly advanced.
6. Vertical Bark Cracks
In addition to splitting from callus formation, you may see long vertical cracks in the bark that expose the reddish or brownish larval galleries underneath. These cracks often appear on the south or west-facing side of the trunk first, where bark temperatures fluctuate more.
Comparing EAB Signs to Other Ash Tree Problems
Not every symptom of canopy decline is caused by EAB. Minnesota ash trees can also suffer from ash yellows, verticillium wilt, drought stress, and anthracnose. The table below can help you distinguish between common issues.
| Symptom | Emerald Ash Borer | Drought Stress | Verticillium Wilt |
|---|---|---|---|
| Canopy dieback pattern | Starts at top, progresses downward | Uniform thinning throughout canopy | Often one-sided or in a single branch |
| Bark damage | D-shaped exit holes, S-shaped galleries | None specific | Streaking in sapwood when cut |
| Woodpecker activity | Significantly increased | Normal levels | Normal levels |
| Epicormic sprouting | Common, especially at trunk base | Rare | Occasional |
| Progression speed | Tree death in 2 to 4 years | Variable, often recoverable | Slow, can take years |
What to Do If You Suspect EAB on Your Property
If you spot one or more of these signs on an ash tree in Minneapolis, St. Paul, or the surrounding metro, it is important to act quickly. A professional tree health assessment can confirm whether EAB is present and how advanced the infestation is. In many cases, trees caught in the early stages can be treated with systemic insecticide injections, but once more than 30 to 50 percent of the canopy has died back, treatment is rarely effective and removal becomes the safer, more practical option.
Dead and dying ash trees also become structurally unstable relatively quickly, since EAB damage weakens the wood and makes limbs prone to sudden failure. This is a serious safety concern for trees near homes, driveways, and power lines. Our tree removal team regularly handles EAB-related removals throughout Hennepin, Ramsey, and Anoka Counties, using proper techniques to safely take down compromised trees without damaging nearby structures or landscaping.
If your ash tree is still in relatively good health but showing early stress signs, targeted tree trimming to remove dead or dying branches can sometimes buy time while you evaluate treatment options and reduce the risk of falling limbs in the meantime.
Handling Removal and Cleanup
Once an infested ash tree is removed, the stump can continue to harbor pests and often becomes a tripping hazard or an obstacle for mowing and landscaping. Complete stump grinding is typically recommended after EAB removals, both to eliminate the risk of residual insect activity and to reclaim usable yard space. Grinding stumps down below grade also allows for easier replanting if you decide to replace the ash tree with a more resistant species down the line.
It is also worth noting that Minnesota has firewood movement restrictions in EAB-quarantined counties, which now includes most of the Twin Cities metro. Wood from removed ash trees should not be transported outside the local area, since this is one of the primary ways EAB spreads to new regions.
Prevention and Early Detection Tips
- Inspect ash trees each spring and summer, focusing on the upper canopy and trunk for D-shaped holes.
- Schedule an annual tree health assessment, particularly if your property is within a mile of a known EAB detection site.
- Avoid moving firewood across county lines, especially from quarantined areas.
- Consider preventive insecticide treatment for high-value ash trees before symptoms appear, since treatment is far more effective before infestation takes hold.
- Diversify your landscape by planting non-ash species if you are replacing a removed tree, to reduce future vulnerability to a single pest.
Frequently Asked Questions
How can I tell if my tree is an ash tree in the first place?
Ash trees have compound leaves with 5 to 9 leaflets arranged opposite each other on the stem, diamond-patterned bark on mature trees, and distinctive brown, paddle-shaped seeds that hang in clusters. If you are unsure, a tree health professional can identify the species quickly during an on-site visit.
Can an infested ash tree be saved once EAB is confirmed?
It depends on how far the infestation has progressed. Trees with less than 30 percent canopy loss often respond well to systemic insecticide treatments applied by a certified applicator. Once canopy loss exceeds 50 percent, the tree’s chances of recovery drop significantly, and removal is usually the safer and more cost-effective choice.
How much does EAB treatment typically cost compared to removal?
Preventive or early-stage treatment is generally billed per diameter inch of the trunk and needs to be repeated every 1 to 2 years, so costs add up over the tree’s remaining lifespan. Removal is a one-time cost but varies based on tree size, location, and site access. A tree health assessment can help you compare the long-term costs of each option for your specific tree.
Is emerald ash borer dangerous to humans or pets?
No, EAB poses no direct threat to humans, pets, or other plants. The danger comes from the structural instability of dead and dying ash trees, which can drop large limbs or fail entirely without warning, especially during storms or high winds common in Minnesota.
What should I do if a dead ash tree becomes a hazard during a storm?
If a storm damages or destabilizes an ash tree that has already been weakened by EAB, do not attempt to handle it yourself. Contact an emergency tree service right away for a safe, prompt assessment and removal before the situation worsens.
If you have noticed any of these warning signs on an ash tree in Minneapolis, St. Paul, or anywhere in Hennepin, Ramsey, or Anoka County, do not wait until the tree becomes a safety hazard. Contact Dynasty Tree Experts today to schedule a tree health assessment and get expert guidance on treatment, removal, or stump grinding options tailored to your property.
TITLE: Signs Your Ash Tree Has Emerald Ash Borer in Minneapolis