How to Spot Emerald Ash Borer Signs in Iowa Trees
Last Updated: October 31, 2026
Quick Summary
Look for top-down thinning in the canopy, D-shaped exit holes about one-eighth inch across on the upper trunk, and serpentine galleries under loose bark. Woodpecker flecking and epicormic sprouts add clues. One sign alone is not proof, but two or more together mean the emerald ash borer should be considered.
Canopy thinning that starts at the top and moves downward is one of the most useful clues.
Exit holes are D-shaped and about one-eighth inch across, concentrated on the upper trunk and larger branches.
Serpentine galleries wind under loose bark; only lift bark that is already peeling.
Woodpecker flecking alone does not confirm infestation, so check for exit holes and galleries too.
Photograph symptoms with dates and a scale, then repeat the inspection in two to three weeks.
Table of Contents
Why Iowa Ash Trees Need a Closer Look
Emerald ash borer is an invasive beetle that kills ash trees, and Iowa homeowners are right to watch for it.
This guide shows you what to look for, where to look, and what to do next.
Emerald ash borer is a small, metallic green beetle native to Asia. Its larvae feed under the bark, cutting off the tree's flow of water and nutrients. Over time, that feeding girdles the tree and kills it.
Emerald Ash Borer Symptoms to Check in the Canopy
The canopy is often the first place symptoms show. Look at the top and outer branches of the tree from a short distance. Compare what you see to how the tree looked in previous years.
Canopy thinning and top-down dieback
Thinning usually starts at the top of the tree and moves downward. You may see bare branches near the crown while lower branches still have leaves. This top-down pattern is one of the more useful clues.
Dieback means branch tips are dying back. Check whether dead twigs are scattered or concentrated in the upper crown. A few dead twigs can happen for many reasons, but steady thinning from the top is more suspicious.
Yellowing leaves, early leaf drop and epicormic sprouts
Leaves may yellow or drop earlier than normal in late summer. Premature leaf loss on a single section of the tree is worth noting.
Epicormic sprouts are small, leafy shoots that grow from the trunk or main branches. A tree under stress may send these up as a survival response. If you see many sprouts along the trunk, the tree may be struggling. Treat that as a reason to look further, not as proof of infestation by itself.
Emerald Ash Borer Exit Holes and Serpentine Galleries
Exit holes are one of the clearest signs of emerald ash borer. Adult beetles leave the tree through round or D-shaped holes, usually about one-eighth inch across, in the bark.
To check for exit holes:
Walk around the trunk and look at the bark from several sides.
Focus on the upper trunk and larger branches.
Look for small, clean holes that appear to be pushed outward.
Note whether the holes are concentrated in one area or spread widely.
Serpentine galleries are the winding tunnels larvae create just under the bark. You can see them by gently removing a small piece of loose bark.
Watch out: Many people mistake other insect holes for emerald ash borer exit holes. Compare the shape and size carefully before drawing conclusions.
Woodpecker Damage on Ash Trees and What It Signals
Woodpeckers feed on emerald ash borer larvae, so woodpecker activity can point to an infestation (Emerald Ash Borer). Look for bark that is flecked, torn, or stripped in small patches. You may see fresh bark chips at the base of the tree or on the ground below.
Woodpecker damage alone does not confirm emerald ash borer. Birds also forage on other insects and may peck at trees for other reasons. Still, repeated feeding marks on an ash tree are worth investigating alongside the canopy and exit hole signs.
Telling Emerald Ash Borer Apart From Drought, Disease and Other Pests
Emerald ash borer symptoms overlap with several common ash problems, and no single sign proves infestation. The useful skill is comparing patterns: where damage appears, how it progresses, and what else is present on the tree. Use the comparison below to narrow the possibilities before you call anyone.
Problem | Where it shows up | What you typically see | What helps confirm it |
Emerald ash borer | Upper crown first, then downward; upper trunk and large branches | Top-down thinning, D-shaped exit holes about one-eighth inch across, S-shaped galleries under loose bark, heavy woodpecker flecking, epicormic sprouts | Two or more signs together, especially exit holes plus galleries |
Drought stress | Whole tree, often many trees on the same street or block | Uniform thinning, leaf scorch along margins, early leaf drop, recovery after sustained rain | Symptoms ease after watering or rainfall; no exit holes or galleries |
Ash yellows | Scattered branches, often one side first | Slow decline, witches' brooms (dense twig clusters), abnormally small leaves, greenish bark on stressed limbs | Lab testing; brooms and stunting without beetle holes |
Anthracnose and leaf spots | Leaves and young twigs | Brown or tan blotches, distorted leaves, twig dieback after wet spring weather | Leaf symptoms dominate; tree often refoliates |
Lilac/ash borer | Lower trunk and base, near soil line | Round holes roughly one-quarter inch across, sawdust-like frass at the base, bark staining | Holes are larger and lower than EAB exit holes |
Ash bark beetles | Trunk and branches | Small round holes, fine sawdust, galleries that branch rather than wind in S-curves | Gallery shape and hole shape differ from EAB |
Woodpecker feeding alone | Trunk and branches | Flecked or stripped bark, bark chips at the base | Birds also feed on other insects; look for exit holes and galleries too |
A few practical rules cut down on misidentification:
Location matters. Emerald ash borer exit holes concentrate on the upper trunk and larger branches. Lilac/ash borer holes cluster near the soil line.
Shape matters. EAB holes are D-shaped and about one-eighth inch across. Round holes of a different size point elsewhere.
Pattern matters. EAB galleries wind in S-curves just under the bark. Bark beetle galleries branch.
Timing matters. Drought and anthracnose often track weather; EAB damage keeps progressing year over year.
Count the signs. One symptom is a reason to look closer. Two or more together, especially exit holes plus galleries or heavy woodpecker flecking, raise the odds substantially.
Pro Tip Photograph each symptom with a date and a reference object (a coin or ruler works) so a certified arborist or extension office can review the images before visiting.
If your comparison points to EAB, move to the inspection steps below and then to confirmation. If it points to drought or disease, a certified arborist can still help you decide whether the tree needs water, pruning, or treatment.
Step-by-Step Inspection Timing and Process for Iowa Homeowners
A good inspection is a sequence, not a single glance. Work from a distance inward, use the right tools, and record what you see so you can compare over time. The steps below are written for a homeowner doing a safe visual check from the ground.
What to bring
Binoculars for the upper canopy
A flashlight for shaded trunk areas
A small hand lens or magnifier
A tape measure for trunk diameter
A notebook or phone for dated photos
A coin or ruler for scale in photos
Gloves if you handle loose bark
Safe inspection sequence
Stand back and scan the whole tree. From 20 to 30 feet away, look at the crown from two or three angles. Note thinning, dead tips, and whether decline starts at the top.
Check the canopy with binoculars. Look for yellowing, early leaf drop, and bare branches in the upper crown. Compare to how the tree looked in prior years.
Walk the trunk in a full circle. Look for D-shaped holes about one-eighth inch across, especially on the upper trunk and larger branches.
Look for epicormic sprouts. Note leafy shoots emerging from the trunk or main branches, and whether they cluster on one side.
Check for woodpecker activity. Look for flecked or stripped bark and fresh chips at the base. Note how recent the damage appears.
Inspect only loose bark. Gently lift bark that is already peeling and look for S-shaped galleries packed with sawdust-like material. Do not pry off tight bark on a living tree.
Measure and record. Note trunk diameter at about 4.5 feet, take dated photos with scale, and write down each symptom and its location on the tree.
Repeat in two to three weeks. Progression is one of the most useful clues.
Watch Out Do not climb the tree, use a ladder near power lines, or strip large sections of bark. Ground-level visual inspection plus dated photos is enough to support a professional assessment.
Timing through the year
April: Watch for woodpecker flecking as larvae resume feeding; bark chips may be fresh.
May through July: Adult beetles emerge, so fresh D-shaped exit holes are most likely to appear. This is the best window for hole checks.
July through September: Canopy thinning, yellowing, and early leaf drop become easier to see; epicormic sprouts often appear on stressed trees.
October through March: With leaves down, dead branches and woodpecker damage are easier to spot; loose bark may reveal galleries.
Confirming and reporting
If you record two or more signs, do not wait for the tree to decline further. Options for confirmation include:
A certified arborist who can assess the tree and, if needed, sample bark or capture a suspect beetle.
Your county extension office, which can help identify specimens and point you to current reporting steps.
State forestry resources for guidance on reporting and on firewood movement rules that slow the spread.
When you contact any of these, have your dated photos, trunk diameter, address, and a short description of the signs ready. That information speeds up review and helps confirm whether a site visit is warranted.
Inspect from a distance inward, record dated photos with scale, check only loose bark, and repeat the inspection in two to three weeks. Two or more signs together justify a professional confirmation.
Emerald Ash Borer Treatment Options and Your Next Step
If you confirm emerald ash borer, you have options. Treatment choices depend on the tree's size, health, and location.
Removal decisions matter too. A badly declining ash can become a hazard, especially near structures or walkways. Dead or structurally weak limbs can fall without warning.
Your next step is a professional evaluation. Anderson Tree Care can help you assess your ash trees. For current pricing, contact us directly, since costs depend on the tree, access, and the work needed. Call or text us for an estimate.
Frequently Asked Questions
What are the first signs of emerald ash borer in an ash tree?
The earliest signs usually appear in the upper canopy. Look for thinning leaves, small patches of dieback at the top of the tree, and yellowing foliage that drops earlier than normal. Sprouts may later emerge along the trunk and lower branches as the tree responds to stress. Because these symptoms also resemble drought stress, confirm them by checking the bark for D-shaped exit holes and serpentine galleries before drawing conclusions.
How can I tell if my tree has emerald ash borer?
Start with a visual inspection of the trunk and canopy. Adult beetles leave D-shaped exit holes about one-eighth inch across, and larvae create S-shaped galleries under the bark. Peel back a small section of bark at the base of the trunk if you see flaking. Woodpecker activity and bark flecking are also strong indicators. If you find several of these signs together, contact your state forestry or extension office to confirm the infestation.
Do woodpeckers indicate emerald ash borer in a tree?
Often, yes. Woodpeckers feed on emerald ash borer larvae beneath the bark, so they tend to peck at ash trunks and upper branches when larvae are present. The damage looks like scattered bark removal and shredded patches. Woodpecker activity alone does not prove an infestation, but combined with canopy thinning or exit holes it is a meaningful warning sign worth investigating promptly.
What should I do if I find signs of emerald ash borer?
Document what you see with clear photos of the canopy, trunk and any exit holes. Avoid moving firewood, since that is a common way the beetle spreads. Confirm the findings through your county extension office or the Iowa Department of Agriculture and Land Stewardship. Then decide on treatment or removal with a certified arborist, since heavily infested trees can become hazardous. Anderson Tree Care can inspect your trees and discuss options; call or text for an estimate, and pricing depends on tree size, location and the work required.
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