Emerald Ash Borer: Is Your Ash Tree Already Dead?
The beetle that has killed 100 million ash trees. How to tell if yours is infested, treatment options, and when to give up.
The Scale of the Problem
The emerald ash borer has killed more than 100 million ash trees in North America since it was first detected in Michigan in 2002. It is now confirmed in 36 states and five Canadian provinces. There is no native predator that keeps it in check. Left untreated, an infested ash tree is dead within three to five years. The USDA estimates the total economic damage at $12.7 billion and counting. If you have an ash tree on your property and you live east of the Rockies, this insect is your most serious tree health threat.
How to Tell If Your Tree Is Infested
The first sign is usually canopy thinning starting at the top of the tree. Branches in the upper crown die back and you notice more sky showing through than last year. Epicormic sprouting, those desperate little shoots growing directly from the trunk, often follows. Woodpecker damage increases because the birds are feeding on the larvae under the bark. If you peel back a piece of bark you may see the distinctive S-shaped larval galleries etched into the wood surface. D-shaped exit holes about an eighth of an inch wide on the bark surface are the definitive sign.
Treatment vs Removal
Emamectin benzoate trunk injection is the most effective treatment, providing two years of protection per application. It costs $200 to $400 per treatment depending on tree size. For a large healthy ash in a prominent location the math works. At $200 per treatment every two years that is $100 a year to preserve a tree that would cost $2,000 to $4,000 to remove. Treatment must begin before the tree has lost more than about 30 percent of its canopy. After that point treatment is unlikely to save it and you are better off spending the money on removal and replanting.
When to Give Up
If your ash has lost more than half its canopy, has heavy bark splitting, shows extensive woodpecker damage on the trunk, or has been dead for more than a year, treatment will not help. Dead ash trees become brittle very quickly, much faster than other species. A dead ash can become hazardous within a year or two, with branches snapping off in light winds. Do not wait. Dead and heavily infested ash trees should be removed promptly, especially near houses, driveways, and sidewalks.
What to Plant Instead
If you are removing an ash and want a replacement with a similar shape and growth rate, consider Kentucky coffeetree, hackberry, or swamp white oak. These are all native species that tolerate a wide range of soils and are not currently threatened by any major pest or disease. Avoid planting another ash. Even EAB-resistant cultivars like Manchurian ash crosses are not truly immune, just more tolerant. The smart money is on diversity. Plant something your neighborhood does not already have a lot of.
Frequently Asked Questions
How do I know if my tree is an ash?
Ash trees have compound leaves with 5 to 9 leaflets arranged in opposite pairs with one leaflet at the tip. The bark on mature trees has a distinctive diamond pattern of interlocking ridges. If you are not sure, send a photo to your county extension office. They will identify it for free.
Is there a quarantine on ash wood?
Many states have quarantines restricting the movement of ash wood, firewood, and nursery stock. Moving firewood is one of the primary ways EAB spreads to new areas. Buy firewood locally and burn it where you buy it.