The tiny insect expected to kill most of the ash trees in Vermont continues its advance, infesting trees in over a quarter of the state's towns.
“We expected that it would be like popcorn across the state, where we pick up detections here and there based on the way that people move wood, which we try to prevent,” said Joshua Halman, forest health program lead at the state Department of Forests, Parks and Recreation.
And that’s exactly what happened. First spotted in a remote forested area in the town of Orange in 2018, the insect has since spread to 68 towns in 13 counties — only Essex County in the Northeast Kingdom has been spared so far.
The emerald ash borer will continue to spread throughout the state, but it is possible to slow its advance, giving towns time to prepare.
“Although we do have emerald ash borer in 13 of those 14 counties, when you break it down by town, you can see that there’s quite a bit of Vermont that does not have the EAB detected, so slowing the spread of it is very important,” Halman said.
A tiny green menace
The emerald ash borer is an invasive species that preys on ash trees. It was first spotted in the US in 2002, though it was likely in the country at least a decade earlier.
Flight season for the emerald ash borer, when the insect lays its eggs on the outer bark of ash trees, runs from June 1 to Sept. 30. It’s in the species’ larval stage that the emerald ash borer lives up to its name, devouring the inner bark and cambium, which circulate sugars generated through photosynthesis and produce new wood and bark, respectively.
Without the ability to transport nutrients, the trees gradually die, becoming a potential hazard when they collapse.
Though slow, an infestation will gradually kill almost every ash tree the insects reach. Some trees can be protected with proactive treatment, but it’s expensive. The most that can be done now is slowing the spread — and there’s still plenty of spread to be slowed.
That’s because, absent human intervention, infestations only spread 1-2 miles a year — the emerald ash borer doesn’t fly very far. But it can travel far more quickly through the transportation of infested wood.
Federal restrictions on the transport of ash wood were not effective in halting the insect’s advance and were lifted in 2021. Vermont does not allow people to bring untreated firewood from out-of-state. For in-state wood, the forestry department recommends using firewood from infested areas near where it was harvested, particularly during the emerald ash borer’s flight season.
There is another federal program to slow the emerald ash borer, though: parasitoid wasps, which target the insect’s larvae. They’ve been in Vermont since 2020, which is still too early to gauge an impact.
“The goal of that program is to have those parasitoid populations be self-sustaining so that they can give the next generation of ash trees a fighting chance to reach maturity,” Halman said, noting that at least one site has reached that goal.
There are several ways to identify the presence of the emerald ash borer. The state forests department uses two types of traps. Prism traps are placed on ash trees, attracting the emerald ash borer and capturing it with glue. A somewhat more invasive strategy is creating a trap tree by peeling the bark around a tree (a method known as girdling) early in the season to attract emerald ash borers, which seem to prefer stressed trees. At the end of the season, the department cuts the tree down to inspect for signs of infestation.
Forests and roadways Ash trees make up about 5% of Vermont’s forests statewide, but that varies a lot from forest to forest. The emerald ash borer won’t result in a barren landscape – just a different one.
“It’s not that we’re not going to have forests anymore in Vermont; we have a lot of species that are mixed in there,” Halman said. “But we do expect mortality to be present on the landscape in the coming years.”
For urban ash trees, things are more complicated. Many towns planted ash trees in place of elm, which experienced its own mass die-off last century as a result of Dutch elm disease. Some towns have hundreds of ash trees within the public right-of-way, the area on and around town highways in which the town has the right to, among other things, manage trees.
That leaves towns with tough choices on how to spend their limited funding, especially since grant money from the U.S. Forest Service, which previously helped pay for surveys and removal, have dried up.
“Nationally, emerald ash borer has been around for a while. And so even though we’re really on the cusp of EAB infestation in Vermont, many states are past it, and so the funding is challenging,” said Joanne Garton, technical assistance coordinator for the state’s Urban & Community Forestry Program. “It’s sort of like we’re late to the party.”
For trees on private property and outside the public right-of-way, it’s up to property owners to decide what to do with their ash trees.
Landowners have a couple of options for dealing with ash trees, said former Chittenden County Forester Ethan Tapper. Trees that could be hazardous if they fall need to be either treated or cut down before they’re killed. Insecticide treatment needs to be done every 1-2 years by a professional indefinitely, meaning most people will probably have to have their trees chopped down. Landowners hoping they can selectively chop some trees to protect others are, unfortunately, in for bad news.
“Cutting trees is not going to protect any other trees from the emerald ash borer. It’s not something where we can just lower the population enough and the emerald ash borer won’t find your ash trees or anything like that,” Tapper said. “If you do want to cut a tree, it’s because it either could be a hazard or because you want to capture some of the value in that tree before it dies.”
At the same time, the fact that a small number of ash trees do survive, becoming “lingering ash,” means there is some value in leaving them alive – but trees killed by the emerald ash borer have no sale value, and their fragility makes them much more dangerous to remove.
Have questions, comments or tips? Send us a message. Or contact the reporter directly at corey.dockser@vermontpublic.org.
