An invasive insect has conquered Orange County’s ash trees

An adult emerald ash borer. The invasive species has ravaged ash trees across North America. Photo courtesy Courtney Johnson and N.C. State.


By Michelle Cassell
Assignment Editor

ORANGE COUNTY — Experts say it is safe to assume that an ash tree on a property in Orange County is dead or dying because of an invasive insect called the emerald ash borer.

“Most ash trees in Orange County are already infested or will be infested soon,” North Carolina State University Assistant Professor Kelly Oten said.

Forestry experts in Orange County discovered the insect in 2016. Since then the beetle has spread fast, and trees have gone untreated, enabling the bug to cause massive destruction to ash trees native to Orange County.

“If someone has an ash tree on their property, consider treating it because, as of right now, that is the only successful way we can tell people to try and save their trees,” Oten said.

Once emerald ash borers start attacking a tree, they die in three to five years. Oten said as the tree’s health declines, insecticides become less effective..

“If they have a tree that they want to save, they should start treating it as soon as possible,” she said.

Damage left by emerald ash borers beneath tree bark. Photo courtesy Kelly Oten.

The insect is a small metallic green beetle native to large sections of Asia and it has become North America’s most destructive invasive species. The insect was first detected in Michigan in 2002 and has since spread to 35 states and five Canadian provinces, killing millions of ash trees, according to an N.C. State fact sheet .

The beetle larvae feed on the inner bark of ash trees, disrupting the flow of water and nutrients and ultimately killing the tree.. The adult beetles feed on leaves and lay their eggs on the bark and reproduce rapidly. It can be difficult to notice the damage to a tree until it is too late.

“On big ash trees where all the canopy is up high, they’ll typically lay their eggs on the tree’s wood up high, and those eggs hatch. And it’s the larvae that start tunneling their galleries under the bark and destroying the tissue under the bark, and that’s what kills the tree,”said Craig Nishimoto, founder of Treeist tree service in Chapel Hill and a certified master arborist, adding if the damage is visible low on a tree it is probably too late.

When it was first discovered, the beetle  was spreading so quickly in the United States that firewood was quarantined because it could harbor beetles.

“Property owners would see this declining ash tree in their yard and maybe they don’t know about the EAB for a problem,” Oten said. “So they would cut the tree down, cut it up in firewood, and if they go camping the next weekend, they might bring it with them. So, those beetles stay in that wood and if they’re brought to a new place, they emerge and infest ash trees at the new location.That moves the beetle hundreds of miles or however many miles, much faster than its natural spread is capable of.”

This resulted in a ban on firewood in many North Carolina state parks that has since been lifted after determining that the ban is no longer effective because of the prevalence of the insects.

“Unfortunately, if you’re in Chapel Hill, it’s likely too late to start treatments,” Nishimoto said.  We’d be very optimistic if people had learned about it three years ago. Right now. We’re very pessimistic about the success rates.

Most of Nishimoto’s Chapel Hill treatments for ash trees began two years ago. His arborists are returning for the second or third rounds of treatments on the same trees. The injections must be done every few years to stave off the bugs.

“The EAB population has exploded,” he said.So they’re everywhere and just gobbling up everything. We would be shocked if, in Chapel Hill, we found a tree that the EAB has not already damaged.”

According to the N.C. Extension Gardener Plant Toolbox, the North Carolina Ash tree, or the White Ash or Biltmore Ash, can be identified by its opposite branching pattern and compound leaves that typically have 5 to 9 leaflets. The leaves of this tree are dark green on top and lighter green on the bottom, with a toothed margin. The bark on mature trees is gray and furrowed, with diamond-shaped patterns. The tree produces winged seeds, known as samaras, in the fall. The North Carolina Ash tree is a tall, deciduous tree that can grow up to 80 feet tall.

Nishimoto said arborists should be able to identify ash trees for property owners.

Typically, Nishimoto informs people they have a problem because the arborist sees the ash trees on their property and says, “Hey, heads up.”

“There’s a lot of information from sources without interest in making money. Most tree services should provide free estimates to identify your trees,” he explained. Nishimoto explained.

Many communities have residents that know how to identify trees or garden clubs as resources as well.

If a tree is too far gone, Nishimoto recommends letting it die and deteriorate on its own as long as it does not pose a threat to nearby buildings, but removing decaying ash trees in densely populated areas is expensive and requires special equipment.

For trees that can still be saved, Oten pointed to creating a treatment according to a guide provided by the North Carolina Forest Service.

“It’s called a soil drench,” Oten said.“You could go to a big box store like Lowe’s or Home Depot, buy this chemical, mix it up, and then drench it around the tree’s base.”

The tree absorbs the chemical mix, which is toxic to the beetles, but it also prevents the tree from becoming a home to non-invasive insects.

The outlook is bleak, but scientists are not giving up.

“I have a Ph.D. student looking at this phenomenon called lingering ash,” Oten said. “ When the Emerald Ash Borer comes through an area, killing 99.9% of the ash trees, once in a while, you see one remaining 0.1% left. They’ve dubbed this finding lingering ash,” she explained.

Researchers believe the survivors possess genetic resistance to the insect, which may provide a route to breed trees for replanting.

Another avenue of control is biological. Entomologists and researchers are seeking native species that could be used to control the insects. Oten said so far a dozen species show some promise.

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2 Comments on "An invasive insect has conquered Orange County’s ash trees"

  1. Thank you for this informative story.

  2. Thank you so much for this excellent and informative article. We have had our ash trees treated so they will not fall victim to this invasive insect. Trees give cooling shade and protect us against climate change. Hoping to be “tree huggers”for many years to come!

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