Like it or not, Vermont officials agree: The emerald ash borer is here to stay.
First detected in Vermont in early 2018, the invasive, ash tree-killing beetle has spread to 11 of the state’s 14 counties, and further spread is inevitable, said Kathy Decker, forest protection health manager for the Vermont Department of Forests, Parks and Recreation.
Now, the challenge is how to best direct state resources to protect the trees that are left.
In January, the federal government removed domestic quarantine regulations for the emerald ash borer, citing the beetle’s presence in 35 states and the District of Columbia as evidence of the policy’s ineffectiveness.
Vermont is unlikely to adopt a quarantine of its own. Instead, it will try to slow the infestation through education and outreach, rather than through regulation, Decker said.
“What do we want to put our effort into: preventing something that we’re not actually going to be able to prevent?” Decker said. “Or trying to educate people, slow that spread and get some other things in place to help manage EAB in the long run?”
The emerald ash borer, named for its shiny-green appearance, is an invasive species of insect native to some regions of Asia. It was first detected in the United States in Michigan in 2002.
The borer is known, lays eggs in ash tree bark. As the larvae feed underneath the bark, they cut off water and nutrients to the tree. The mortality rate for infested trees is nearly 100%, and most infested trees are dead within five years.
Between 5% and 7% of Vermont’s trees are estimated to be some variety of ash, or around 150 million. But the trees aren’t evenly distributed, Decker said, meaning some areas of the state could be hit much harder than others.
The borer doesn’t go very far on its own — only a mile or 2 each year — but the human movement of untreated firewood or other wood products has greatly accelerated the spread.
“Firewood seems to be the method by which the emerald ash borer has moved all across the country in as rapid a timespan as it did,” said Judy Rosovsky, the state entomologist.
The borer quickly infested Michigan’s forests and killed tens of millions of trees despite the state’s internal quarantine. Michigan repealed the quarantine in 2018; what was the point?.
New Hampshire, which detected EAB in 2013, ended a similar quarantine the same year.
Vermont still has regulations against bringing firewood into the state from other locations unless it’s been heat treated — placed in a kiln at high temperatures for sterilization.
Federal regulations control the entry of ash wood over the Canadian border into states including Vermont, but Rosovsky said those rules might change as regulation proves futile.
“We’re not saying we’re done — we still have our external firewood quarantine — but there’s nothing we can really do to stop [the emerald ash borer] from entering the state,” Rosovsky said.
‘No magic bullet’
Since regulation hasn’t worked, the state has looked into other means of slowing the spread of the emerald ash borer.
Vermont is fortunate to have had a 16-year head start. As the borer headed east from Michigan, the U.S. Department of Agriculture set up a laboratory to rear parasitoids, a type of parasitic insect, to act as a biocontrol measure on the borer population.
The wasp-like parasitoids were introduced in Michigan in 2007 and were released in Vermont in 2020 at two sites, L.R. Jones State Forest in Plainfield and on private land in Grand Isle County.
The parasitoids pierce ash tree bark and lay eggs inside emerald ash borer larvae. Those eggs hatch into larvae, which consume and kill the EAB host.
The state will add two new variants of parasitoids to its arsenal this year. One has a longer ovipositor and can penetrate thicker bark. The third lays its eggs inside the EAB eggs rather than the EAB larvae.
Extensive lab testing has provided evidence that the wasps don’t affect any other insect group, said Josh Halman, forest health specialist with the Vermont Department of Forests, Parks and Recreation.
It’s an exciting development for biocontrol methods, which have long been used to fight invasive species, but not a solution to the spread of EAB.
“The real goal of this program is not to eradicate the emerald ash borer from the landscape,” Halman said. “Unfortunately it’s here, and there’s been no signs that biocontrol efforts are going to fully eradicate the insects.”
Instead, foresters hope the parasitoids can keep the borer population at manageable levels in areas where there are saplings and seedlings.
“It gives them a fighting chance to become mature trees,” Halman said.
There’s also education. The website vtinvasives.org was set up as a one-stop shop for residents and local leaders to find out more about the emerald ash borer, as well as other insects.
The Department of Forests, Parks and Recreation still inspects and monitors the ash tree population for evidence of new infestations, and residents can report sightings to the department themselves.
The state also monitors what Rosovsky calls Operation Purple Trap, which refers to purple, prism-shaped boxes hung in trees that emit scents to attract the borer. The boxes are coated in a nonlethal glue, which allows for safe inspection.
Sightings in the field or in the traps, as well as community reports, are used to update a map of the borer’s infestation across the state. It isn’t known how many trees the EAB has killed in Vermont, but for now, Decker said, “the death is not widespread.”
What can I do?
The first point is basic: Don’t move untreated firewood, even within Vermont.
It’s fine to use local wood for home heating or campfires, but the state advises against moving firewood outside a 25-mile radius. The less, the better. That helps prevent emerald ash borers or other harmful insects from reaching areas that haven’t been infested yet.
Some towns are taking preventive measures on their own.
The Shelburne Tree Committee created a digitized inventory to monitor the size and condition of local ash trees. About 85% of the trees are listed as in fair or good condition, and the state-run map doesn’t show signs of an EAB outbreak in Shelburne.
Rutland devised a two-pronged plan: Preemptively cut down healthy ash trees and replace them with a different species, and inoculate the remaining 100 ash trees with a chemical treatment to stave off the borer.
Heritage Tree Care, a tree company based in Essex, uses a product called TREE-äge R10. The chemical mixture is injected into the tree’s vascular system — ideally between May and September, when the sap is most active.
The product is harmless to bees and birds, according to Patrick Grant, owner and manager, and keeps healthy trees from being infected with about a 95% success rate.
Trees must be treated every two years to maintain EAB immunity. That makes the process more expensive as time goes on and is unlikely to save a large number of Vermont’s ash trees. Treating every ash tree this way would be impractical, Grant said.
“But certainly, if you have a special ash tree on your property that you really love, it seems like the only way you’re going to save it is by injecting it,” Grant said.
A small number of ash trees in Vermont might have a natural resistance to the borer, Rosovsky said, and the state would look to breed those strains to create the next generation of ash trees.
Vermont Urban and Community Forestry program — a partnership between the University of Vermont Extension and the Department of Forest, Parks and Recreation — also serves as an educational tool for municipalities and volunteer groups. Ginger Nickerson, the forest pest education coordinator, teaches people how to detect signs of EAB infestation, and how to handle it.
Emerald Ash Borer Awareness Week in Vermont starts May 15. Planned events include free webinars on the state of the infestation, and the environmental and cultural significance of black ash trees. More details can be found on the organization’s events page.
In partnership with the Vermont Land Trust, the Urban Community Forestry program is also collecting memories, stories and poems on what the ash tree means to Vermonters. Residents are welcome to submit their own on the trust’s website.
Foresters and agents hope the combination of biocontrol, education and outreach can at least “slow the spread.”
“I don’t feel like there’s a magic bullet regulation that stops the emerald ash borer,” Rosovsky said.
Residents who think they’ve spotted an infestation of emerald ash borer near them should report it on the Vermont Invasives website.
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