Ash trees and the emerald ash borer

Where it stands in North Carolina

Emerald ash borer was first found in North Carolina in 2013, in Granville, Person, Vance, and Warren counties. In 2015 it was found in many additional counties and a statewide EAB quarantine went into effect. The N.C. Forest Service maintains a tracking map of affected counties, and detections have continued to be announced since.

The quarantine restricts moving harvested ash material out of quarantined areas without a compliance agreement from the NCDA&CS Plant Industry Division, which for a homeowner mostly translates into one practical rule: do not move ash firewood. Moving infested wood is how the insect covers distances it could never fly.

Do you have an ash?

Ash is not as common in Piedmont yards as oak, but it is here, particularly green ash on bottomland and along creeks. Three features together identify it, and you need all three because any one on its own is ambiguous.

• Opposite branching. Twigs and buds emerge in pairs directly across from each other, not staggered. Very few trees do this, and it immediately rules out oak, poplar, sweetgum, and most of what else is in the yard.
• Compound leaves. What looks like one leaf is five to nine leaflets on a single stalk.
• Diamond-patterned bark. Mature ash bark forms a distinct interlacing diamond lattice.

The tree most often confused with ash here is box elder, which is a maple with opposite branching and compound leaves. Box elder leaflets are usually three to five and coarsely toothed, and the tree is generally scruffier and multi-stemmed.

What the borer does

Adults lay eggs on the bark. The larvae hatch and tunnel into the layer of tissue just beneath it, feeding in S-shaped galleries that cut the tree's plumbing. Enough larvae and the tree can no longer move water and food between roots and canopy, which is why the crown dies from the top down.

The N.C. Forest Service describes the timeline plainly: within two years of observing symptoms, most of the crown of the tree will be dead, and complete tree death typically occurs within five years.

Signs to look for, roughly in the order they appear: thinning starting at the top of the crown, sprouts erupting from the trunk and the base as the tree tries to rebuild leaf area, vertical splits in the bark, unusually heavy woodpecker activity stripping bark to get at larvae, and small D-shaped exit holes about an eighth of an inch across where adults have emerged.

Treat or remove

The Forest Service guidance is that insecticide treatment is worth considering for high-value ornamental trees when the beetle is known to be within fifteen miles of the tree, and that re-treatment is required every one to two years. That last part is the crux of the decision. Treatment is not a cure, it is an ongoing commitment for as long as you want to keep the tree, and it needs to start before the crown has significantly declined rather than after.

The questions worth asking yourself: is this a tree you value, is it in good condition now, is it in a position where losing it would matter, and are you prepared to pay for treatment indefinitely. A healthy specimen ash shading a patio is a reasonable candidate. A mediocre ash at the back of a lot is not.

For dead and dying ash, Forest Service guidance is to cut them down and chip, burn, or bury the wood on site to reduce the risk of attack on other trees. Consulting a county forest ranger or a certified arborist before committing either way is the sensible step.

Why waiting costs money

This is the part specific to tree work rather than to forestry, and it is the reason a dead ash is not a job to leave for next year.

Ash killed by the borer dries out and becomes brittle unusually fast. Within a season or two of death, the wood is no longer reliable to climb: limbs snap under a climber's weight without the warning that green wood gives. Once a tree cannot be climbed, it has to be taken down from a bucket truck or a crane, which changes the equipment, the crew, and the price. A standing dead ash that could have been removed by a climber for one number becomes a bucket or crane job for a considerably higher one, and if it is in a back yard where neither can reach, the options narrow further.

So the sequence that saves money is: identify the tree, decide treat or remove, and if the answer is remove, do it while the wood is still sound.

What to plant instead

Anything but ash, and preferably not another single species planted in quantity. The lesson of the borer, and of Dutch elm disease before it, is that monocultures fail together. A yard with a mix of species survives the next arrival better than a yard with six of the same tree. The replanting guide covers reasonable choices for a Piedmont lot.