⚠ High Urgency

Holes in Tree Trunk or Branches

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What It Means Causes Trees Affected How Urgent What To Do Call an Arborist?Regional Notes Related Pests FAQ

What This Symptom Usually Means

Holes in tree trunks can be caused by boring insects, woodpeckers, or decay. Boring insects are the most concerning — they tunnel through the wood that transports water and nutrients, weakening the tree structurally and physiologically. Woodpecker holes are actually a secondary sign — woodpeckers drill into trees to feed on boring insects underneath. The size, shape, and pattern of holes help identify the cause.

Most Likely Causes

Emerald ash borer (EAB)

Leaves distinctive D-shaped exit holes about 1/8 inch wide. Larvae create S-shaped galleries under the bark. Fatal to ash trees within 3-5 years without treatment.

Bark beetles

Tiny round holes (1-2mm) with fine sawdust. Create elaborate gallery patterns under bark. Multiple species attack conifers and some hardwoods.

Clearwing borers

Holes at base of trunk with frass (sawdust-like excrement) pushed out. Common in dogwood, lilac, birch, and ash.

Woodpeckers

Rows of small holes (sapsucker damage) or large irregular excavations. Sapsuckers create orderly rows; other woodpeckers make random holes hunting for insects inside the wood.

Carpenter ants

Smooth, clean galleries in soft or decaying wood. Leave piles of fine sawdust (frass) at base. Do not eat wood — excavate it for nesting.

Natural decay

Large cavities from previous branch failures or wounds that have decayed over time. Common in older trees and not necessarily a sign the tree is unsafe.

Trees Commonly Affected

Ash

Primary target of emerald ash borer — D-shaped exit holes are diagnostic

Pine

Southern and western pine beetle cause rapid decline

Birch

Bronze birch borer targets stressed trees — especially in urban settings

Dogwood

Dogwood borer larvae tunnel in trunk, especially at graft unions

Oak

Two-lined chestnut borer attacks stressed oaks

Spruce

Spruce bark beetle causes declining populations in western forests

How Urgent Is This?

⚠ High Urgency

High. Boring insects can kill a tree within 2-5 years depending on the species. Emerald ash borer and bark beetles are particularly destructive and require prompt treatment or removal decisions. Woodpecker holes are less urgent — they indicate insects are present but the woodpeckers are actually helping by eating them. Large decay cavities should be assessed by an arborist for structural safety.

What You Can Do Right Now

Identify the hole type: D-shaped (EAB), round tiny (bark beetle), round with frass (borers), rows (sapsucker), large irregular (woodpecker/decay).
Check for sawdust or frass at the base of the tree — active borers push debris out as they tunnel.
Peel back a small section of loose bark to check for tunneling patterns underneath.
Note the tree species — this narrows down which borer species is likely responsible.
Check if neighboring trees of the same species show similar damage.
Take clear photos of the holes including something for scale (a coin or ruler).

When to Call a Certified Arborist

Contact a certified arborist if any of these apply:

✓You find D-shaped exit holes on an ash tree (emerald ash borer — treatment decisions are time-sensitive)
✓Multiple trees in your area are showing the same symptoms
✓Large cavities compromise more than a third of the trunk circumference
✓The tree is in a location where failure would endanger people or structures
✓You want a professional assessment of whether the tree can be saved or should be removed

Find an Arborist Near You

State & Regional Differences

Midwest

Emerald ash borer has killed hundreds of millions of ash trees. Treatment is effective if started early. Asian longhorned beetle has been detected in some areas.

Southeast

Southern pine beetle outbreaks cause massive pine mortality during drought years. Ambrosia beetles attack stressed hardwoods.

West

Mountain pine beetle and spruce beetle have killed billions of conifers across western forests, exacerbated by drought and warming temperatures.

Northeast

Asian longhorned beetle eradication zones are active in several areas. EAB continues to spread through ash populations.

Frequently Asked Questions

What does a D-shaped hole in a tree mean?

A D-shaped exit hole about 1/8 inch across is the signature of the emerald ash borer (EAB). It means adult beetles have emerged from under the bark. If you find D-shaped holes on an ash tree, the tree has been infested for at least one year. Contact your state department of agriculture and a certified arborist immediately to discuss treatment options.

Are woodpecker holes bad for trees?

Woodpecker holes themselves rarely harm healthy trees. Sapsuckers create orderly rows of small holes that can girdle branches if severe, but usually the tree compartmentalizes the damage. The bigger concern is what attracted the woodpecker — they are often feeding on boring insects inside the wood, which is the real threat.

Should I fill holes in my tree?

No. Filling cavities with concrete, foam, or other materials was once standard practice but is now discouraged. Fillers can trap moisture, prevent the tree from compartmentalizing decay naturally, and make future assessments difficult. Leave cavities open and let the tree respond naturally.