How fast does emerald ash borer kill ash trees?

Most ash trees die within 3 to 5 years of initial EAB infestation without treatment. In high-population areas where multiple generations of beetles are emerging simultaneously, trees can decline faster — sometimes within 2 to 3 years of first observable symptoms. Trees under stress from drought, poor soils, or other pathogens decline faster than healthy trees. Once infestation is established in a stand, all ash in that stand should be assumed at risk.

At what stage of EAB damage can ash still be harvested for timber?

Ash trees retain merchantable sawlog value through Stages 1 and 2 of EAB damage — when crown dieback is less than 50%, bark is intact, and the wood has not yet begun to stain or check. Stage 3 trees with major crown loss and beginning bark deterioration may still produce some sawlog volume but at lower grades and reduced prices. Stage 4 trees — dead, bark slipping, and showing wood decay — have no sawlog value and are at best pulpwood or firewood.

What is the D-shaped hole in ash bark?

The D-shaped emergence hole is created when an adult EAB beetle chews through the bark to exit the tree. The hole is approximately 1/8 inch (3-4mm) wide with a distinctive D shape — flat side up. Exit holes are one of the most reliable field confirmation indicators for EAB because no other common New York forest pest creates the same D-shaped hole on ash bark. Finding multiple exit holes on a tree confirms active or recent EAB infestation.

Can I tell how many years of timber value I have left?

Not with precision — but a forester can give you a useful assessment. Stage 1 trees with early crown thinning and no exit holes visible may have 2 to 4 years before significant grade decline. Stage 2 trees with epicormic sprouting and visible exit holes may have 1 to 2 productive years remaining. Stage 3 trees may have one season of partial value. The key variable is beetle population density in your area and how many generations have already emerged from your specific trees. Henry Kowalec assesses this during a woodland walk and gives you a direct read on the timing question.

Emerald Ash Borer Damage: How to Tell How Far Gone Your Ash Trees Are

Emerald Ash Borer Damage: A Four-Stage Framework

Understanding where your ash trees fall in EAB’s damage progression determines what your options are. This guide explains the four stages and what each means for timber value, treatment viability, and management decisions.

Want Henry to walk your property and assess your ash stands? Call (845) 754-8242 for a free assessment.

Stage 1: Early Infestation — Full Timber Value Intact

What you see: Thinning in the upper 25% to 33% of the crown. Fine branch dieback at the top of the canopy. Lower branches still fully leafed out. D-shaped exit holes may or may not be visible yet — the infestation may predate adult emergence in the current season.

What’s happening inside: Larvae are feeding in the cambium, but the network of galleries has not yet girdled enough of the tree to cause major visible stress.

Timber value: Full sawlog value. White ash and green ash in Stage 1 produce the same grade and price as unaffected ash.

Options: Chemical treatment is economically viable for high-value specimen trees. Stand-level timber harvest can recover full market value.

Stage 2: Moderate Infestation — Harvest Window Narrowing

What you see: 30% to 50% crown loss. Epicormic sprouting visible on the trunk and major branches. D-shaped exit holes present on mid-trunk bark. Woodpecker activity may be visible.

What’s happening inside: Gallery density is significant. Multiple larval generations have emerged. The cambium is girdled across a substantial portion of the tree’s circumference.

Timber value: Sawlog value still present in trees with intact bark and no internal wood staining. Some grade reduction possible depending on species and individual tree quality. Harvest while in Stage 2 recovers the majority of available value.

Options: Chemical treatment is not cost-effective for most trees at this stage — the damage is too advanced. Timber salvage harvest is the primary management tool. A forester should assess each tree individually.

Stage 3: Advanced Infestation — Grade Decline Begins

What you see: Greater than 50% crown loss. Heavy epicormic sprouting. Bark beginning to crack, loosen, and pull away from the trunk in sections. Heavy woodpecker blonding. D-shaped holes visible across multiple sections of the trunk.

What’s happening inside: The tree is effectively dead or dying. The cambium is largely destroyed. Wood may show early blue stain fungal infection.

Timber value: Declining. Stage 3 trees may still produce some sawlog volume in the lower butt log if bark is reasonably intact and wood is not yet staining. Upper logs grade to pulpwood or lower. Every season of delay in Stage 3 reduces value further as wood deterioration accelerates.

Options: Harvest immediately if any commercial value remains. Do not wait for Stage 4.

Stage 4: Dead and Declining — No Commercial Value Remains

What you see: No living crown. Bark slipping — pulling away from the trunk in sheets when touched. Heavy woodpecker damage. Structural deterioration beginning — branches breaking, lean developing.

What’s happening inside: The wood is dead and decay fungi are establishing. Internal checking and staining are advanced.

Timber value: No sawlog value. Limited pulpwood value if the tree is felled before structural failure, but mills may not accept EAB-killed pulpwood with significant decay.

Options: Salvage for firewood or leave as wildlife habitat if location allows. Stage 4 ash have passed the point of commercial recovery.

Timber Value by Infestation Stage

The progression from Stage 1 to Stage 4 typically takes 3 to 5 years from first infestation, though high beetle populations in some areas can accelerate this timeline. The shift from full sawlog value (Stage 1) to significantly reduced value (Stage 3) can happen within a single growing season.

Landowners who have a woodland assessment done when they first notice symptoms — Stage 1 or early Stage 2 — have the most options. Those who wait until the problem is unmistakable often find they are already in Stage 3.

Henry Kowalec walks ash-affected properties throughout Sullivan, Orange, and Ulster counties and gives landowners a direct assessment of where their trees fall — and what the honest options are at that stage.

Call (845) 754-8242 to schedule a free woodland assessment.

Henry Kowalec — Certified Consulting Forester — Environmental Forest Products, Westbrookville, NY