Although an enormous amount of damage is being done to New Hampshire forests these days by relatively new pests like emerald ash borer and hemlock adelgid, lots of people are appalled by the damage done by a more familiar pest — albeit one carrying a new name.
“Tens of thousands of trees alongside the road. Mostly hardwoods. A stunning sight. We have never ever seen such a shocking occurrence,” wrote John Kiernan in a recent email to the Concord Monitor titled “Damaged Trees on I-89.”
That loss of leaves and similar defoliation in patches of trees, mostly oaks, is due to the caterpillar of the spongy moth, Lymantriadispar. That moth, formerly known as gypsy moth, has been a problem in New England since it was imported in 1869 as part of a failed attempt to establish the silkworm industry here. Its population has ebbed and flowed over the years as part of natural cycles as well as a fungus and viral disease.
New Hampshire hadn’t seen a huge outbreak since the early 1990s – until last year, when more than 30,000 acres were defoliated by spongy moth in various parts of the state. The Concord region largely escaped that outbreak, but it hasn’t escaped this year’s replay.
“It’s definitely around us,” said Robert Farquhar, nursery manager at Brochu Nursery and Landscaping in Concord. “I’ve been keeping an eye on what we have growing in the field, but so far it’s not a problem.”
Looking around Concord, damage is evident.
“It’s kind of patchy, but when it does get in there, it can be bad,” said Ryan Rambeau, tree supervisor for the city of Concord. He noted that a big denuded patch is visible from I-393 toward Epsom and “at Garvins Falls, right before you get to the power line, that’s pretty awesome there. … It looks like fall time.”
Spongy moth caterpillars like oak trees best but will eat other species of trees if they run out of their favorite. “When they start taking on evergreens, the white pines, you know there’s a lot of it,” he said.
Other Concord woods that have been heavily affected include those around Batchelder Mill trails and on Eastside Drive.
The New Hampshire Division of Lands and Forests is performing aerial surveys to estimate the amount of damage from spongy moth, but it is probably greater than last year.
Despite how bad it looks, defoliation doesn’t kill trees unless it happens several years in a row.
“A tree can handle quite a bit of stress. Losing leaves one year isn’t so bad,” said Farquhar.
A tree that is denuded early in the year will sometimes grow some replacement leaves before the summer is over.
However, a year’s defoliation can weaken trees enough to make them vulnerable to other pests or diseases, particularly if it happens during a dry spell like the state is currently seeing.
There’s not much that can be done to help an infected tree.
Outbreaks usually decline because of a fungus called entomophagamaimaiga, as well as a virus that can start killing caterpillars once the population reaches a certain density. The fungus needs moisture, so long dry spells like New Hampshire saw in 2020 through early 2021 can reduce its spread, which is one reason for the current caterpillar outbreak.
The Entomological Society of America changed the name of this moth as well as the name of a species of tropical ant because “gypsy” is considered a derogatory way to refer to the Romani people of central Europe. The name “spongy moth” was chosen because its egg masses resemble a sponge.