Getting to Know the Ash Before the Borer Does

Field note 260819 · August 19, 2026

Some threats arrive with a bang. Emerald ash borer arrives quietly, a small beetle you'll probably never see. It has killed ash trees across much of the country, and it's in Oregon now. As of this August, it hadn't turned up in Benton County.

We have Oregon ash along the creek, so I asked an OSU Extension forester what a landowner should do while there's still time. The answer was simpler than I expected: get to know your ash now.

Why now

When the borer does show up, I want to be able to tell new damage from old. Our ash are already putting up with hot, dry summers, and plenty of drought damage looks a lot like borer damage.

The forester gave me a useful split:

• Signs that could be either: a thinning crown, dying branches, shoots sprouting from the trunk or base, woodpecker damage, and splits in the bark.

• Stronger signs of the borer: small D-shaped exit holes, and S-shaped tunnels under split bark.

You're unlikely to ever catch the beetle itself, which seems a little unfair. The state runs traps, but they can't be everywhere. A landowner who knows their own trees fills in the gaps.

The plan

1. Compare where I think our ash grows with the new state hardwood map.

2. Walk the places where the two disagree, and write down what's really there.

3. Map the ash on the property map, with outlines around the denser stands.

4. Pick a few permanent trees to watch, and take baseline photos and notes on each.

5. Check them again on a schedule.

Not spraying yet

I asked about treating the trees ahead of time. The advice was to wait until the borer is found in the county. The trunk injection has to be repeated every two to three years. Paying for years of protection against a bug that isn't here yet is a hard sell, even to a worrier like me.

Not cutting them all, either

The other advice was to plan the succession now, which sounds grim but isn't. It doesn't mean clearing the ash. It means picking a few trees, or small groups, to remove gradually and planting other suitable species in the openings. Then, if the ash do die, there's already young canopy coming up to take their place.

The first ones I'll look at are the trees that would be hard or dangerous to take down once they're dead, like those leaning over a building or driveway.

If you have ash on your place, this winter is a good time to walk them with a camera. It costs nothing but a walk, and someday those photos may be the only way to know what changed.