Emerald Ash Borer Signs: Is Your Ash Tree Infested?

The emerald ash borer (EAB) has killed tens of millions of ash trees across North America since arriving from Asia around 2002. Pennsylvania, including the Lehigh Valley, has been hit hard. If you have ash trees on your property, here's what you need to know.

First: Do You Have Ash Trees?

Before worrying about emerald ash borer, confirm you actually have ash trees. Ash are commonly confused with other species.

Ash tree identification:

• Opposite branching: Branches grow directly across from each other (not alternating)
• Compound leaves: Each leaf has 5-9 smaller leaflets arranged along a stem
• Diamond-patterned bark: Mature ash have distinctive diamond or X-shaped ridges in the bark
• Seeds: Single-winged seeds in clusters (called "samaras" or "helicopters")

Common ash species in Pennsylvania:

• White ash (most common)
• Green ash
• Black ash
• Blue ash (somewhat resistant to EAB)

Signs of Emerald Ash Borer Infestation

Early Signs (Tree May Still Be Saveable)

Canopy thinning at the top:

• Dieback typically starts in the upper third of the tree
• Leaves appear sparse compared to previous years
• Crown looks "see-through" when other trees are full

Increased woodpecker activity:

• Woodpeckers feed on EAB larvae under the bark
• Look for patches where bark has been flaked off
• Heavy woodpecker damage on an ash tree is a strong indicator

Epicormic sprouting:

• New shoots growing directly from the trunk
• Tree's stress response to losing its canopy
• Often appears as bushy growth low on the trunk

Definitive Signs (Confirms Infestation)

D-shaped exit holes:

• About 1/8 inch wide
• Distinctly D-shaped (flat on one side, rounded on the other)
• Left by adult beetles emerging from under bark
• May be scattered across trunk and branches

S-shaped galleries under bark:

• If you peel back loose bark, you'll see serpentine tunnels
• These are feeding tracks from larvae
• Galleries are packed with sawdust-like frass

Bark splitting:

• Vertical splits in the bark
• Caused by callus tissue forming over galleries
• S-shaped galleries often visible in the splits

Late Signs (Tree Likely Cannot Be Saved)

• More than 50% canopy loss
• Exit holes covering most of the trunk
• Bark falling off in sheets
• Few or no leaves by late spring
• Extensive woodpecker damage throughout

The Timeline: How Fast Does EAB Kill Trees?

Once infested, most ash trees die within 2-5 years. Here's the typical progression:

Year 1-2:

• Infestation begins, often undetected
• Population builds under bark
• Tree may appear healthy or show slight thinning

Year 2-3:

• Canopy thinning becomes noticeable
• Exit holes may become visible
• Epicormic sprouting appears
• Tree still potentially treatable

Year 3-5:

• Severe canopy loss (50%+)
• Extensive exit holes and bark damage
• Tree typically beyond saving
• Death follows shortly

Can Your Ash Tree Be Saved?

The answer depends on how far the infestation has progressed:

Treatment Is Likely Effective If:

• Less than 30% canopy loss
• Tree is otherwise healthy and well-established
• You're willing to commit to ongoing treatment (every 1-2 years)
• The tree's location justifies the cost

Treatment Is Probably Not Worth It If:

• More than 50% canopy loss
• Extensive exit holes throughout trunk
• Significant bark loss
• Tree was already stressed or in decline
• Tree is in a location where removal is inevitable anyway

Treatment Options

Trunk injection (most effective):

• Insecticide injected directly into the tree
• Usually done by professionals
• Lasts 2-3 years per treatment
• Reaches throughout the tree

Soil drench/injection:

• Insecticide applied to soil at base
• Tree absorbs through roots
• DIY products available, but professional application more reliable
• Typically annual treatment

Bark spray:

• Less effective than other methods
• May work for smaller trees
• Requires careful timing

Treatment Cost vs. Removal Cost

This is the calculation every ash tree owner faces:

Treatment costs:

• Professional trunk injection: $100-300 per treatment
• Needed every 2-3 years for the life of the tree
• A tree that lives 30 more years = $1,500-3,000+ in treatment

Removal costs:

• Depends on size and location
• Typically $500-2,500 for most residential ash trees
• One-time cost

Consider treating if:

• The tree provides significant shade to your home (energy savings)
• It's a specimen tree or has sentimental value
• Removal would be extremely expensive or difficult
• You want to preserve mature trees on your property

Consider removal if:

• The tree is already declining
• It's in a problematic location anyway
• You have multiple ash trees (treating all may not be practical)
• The tree isn't particularly valuable to you

If You Don't Treat or Remove

Untreated ash trees will die. But that's not the end of the problem:

• Dead ash become hazardous quickly. The wood becomes brittle and branches fall unpredictably.
• Removal becomes more dangerous and expensive. Dead trees are harder to work with safely.
• Waiting too long can damage property. A dead ash can drop large branches or fall entirely.

If you decide not to treat, plan for removal within 1-2 years of the tree's death—before it becomes a hazard.

Preventive Treatment

If you have a healthy ash tree you want to keep, preventive treatment before infestation is the most effective approach:

• Treatment works best when started before significant damage occurs
• Costs less than trying to save an already-infested tree
• Gives the tree the best chance of long-term survival

The argument against preventive treatment: you're committing to ongoing costs for a tree that might not have been infested for years anyway. Given how widespread EAB is in Pennsylvania, however, it's generally a matter of "when," not "if."

The Bigger Picture

Emerald ash borer has fundamentally changed Pennsylvania's landscape. Millions of ash trees have died, and millions more will. This has implications beyond individual trees:

• Urban tree canopy loss (ash were commonly planted street trees)
• Forest composition changes
• Increased sunlight reaching forest floors (affecting other plants)
• Loss of ash wood products

For homeowners, the practical question is what to do about the ash trees you have. Assess their condition, their value to you, and make decisions accordingly. There's no shame in removing an ash tree that's become a liability—and no guarantee that treatment will work forever.

What To Do Next

1. Identify your trees: Confirm you have ash (not mountain ash or another species)
2. Assess condition: Look for signs of infestation listed above
3. Get professional input: An arborist can confirm EAB and assess treatability
4. Decide on treatment vs. removal based on tree condition and your priorities
5. Act promptly: Waiting makes both treatment and removal harder

If you're unsure whether your ash trees are infested or what to do about them, an arborist consultation is worth the investment. They can give you a clear picture of your options before you commit to treatment or removal.