Year two of spongy moth devastation

SHARON — For the second year in a row, an invasion of spongy moth caterpillars has caused significant defoliation of trees in the Northwest Corner, causing concern among state and local foresters and environmentalists who said a repeat next year could cause mass mortality to stressed trees.

“Sharon, Salisbury, Kent, Cornwall, Norfolk and parts of Goshen just got hammered again for a second year,” said Christopher Martin, Director of Forestry for the state Department of Energy and Environmental Protection (DEEP), in an interview Thursday, June 16.

It’s hard to miss the brown areas lining the upper ridges of the landscape, he said. “It looks more like fall and winter than spring and summer. It is uncanny and unnerving,” said Martin, who also serves as president of the National Association of State Foresters.

Spongy moths, formerly called gypsy moths, have also hatched in the Berkshires and upstate New York, wreaking havoc on outdoor enthusiasts and homeowners, although not to the extent of the destruction in the northern reaches of Connecticut.

Normally, the spongy moth population is low and the damage it does is fairly restricted. However, when it enters into outbreak status, as has happened over the past two years, it is a significant problem. The energy required to refoliate puts significant stress on trees, increasing the risk of tree mortality with each consecutive outbreak.

CAES aerial surveys

Annual forest pest and disease aerial surveys conducted by the Connecticut Agricultural Experiment Station (CAES) documented that spongy moth caterpillars defoliated 156,000 acres in 2020, mostly in the eastern half of Connecticut, and 45,548 acres in 2021, mostly in Litchfield County. (The result of the 2022 annual survey by CAES has not yet been released.)

Martin said that 2021 was the first year of widespread defoliation in northwest Connecticut and most healthy trees refoliated, in part due to sufficient summer rains, which activated a naturally occurring soil-borne fungus that is lethal to only spongy moth caterpillars and normally keeps their population in check.

In outbreaks, the larvae, or caterpillars, emerge in great numbers. By the end of June, they will have stripped bare a majority of trees in forests and yards.

When entering an area being ravaged by the dark and hairy insects, said Martin, you can hear the frass, or caterpillar poop, raining down. “It’s disgusting, quite frankly. You can hear the frass falling. It sounds like rain. It’s just gross.”

Just ask Eileen Fielding, executive director of the Sharon Audubon Center, where “the oaks are getting slammed,” she recently reported.

Fielding said she is especially heartbroken by the defoliation, two years in a row, of a stately oak that graces the entrance to Sharon Audubon.

“We have a magnificent, huge oak tree at the entrance to the center; there was not a leaf on it last year. Same thing this year. It’s completely bare. We are worried that some trees that got hit two years in a row might be weakened and will not survive.”

Helping trees recover

Spongy moth infestations are difficult to control over wide areas and while the state has no plans for widespread aerial spraying, individuals are encouraged to consult with arborists or a licensed pesticide applicator to protect their trees prior to the emergence of caterpillars, or to help trees recover from defoliation.

Tom Zetterstrom, a tree preservationist, environmental activist and fine-arts photographer in North Canaan, noted that one egg mass can contain as many as 500 eggs, resulting in “an exponential expansion, and suddenly we have a dramatic increase in defoliation.”

He said he has not witnessed this level of defoliation in decades. “My observation is that it is as bad as the gypsy moth explosion in 1981, when I remember losing trees in the higher elevation of my woodlands.”

The spongy moths, said Zetterstrom, have their most favored foliage, which are white oaks. “They were immediately and heavily defoliated, followed by red oaks, white oaks, birches, and now they are going on to the elms.”

On a community level, Zetterstrom credited Lisa Carter, superintendent of the Region One School District, for taking proactive measures early in the outbreak. She consulted with local arborist Fred Scoville and sought emergency approval for the treatment of trees at the high school and various grade schools.

“They came up with a strategy of injecting the campus trees, with good success,” Zetterstrom said.

For those trees that do become defoliated, he said, it is important to feed them nutrients and keep them watered “to encourage new leaf pull-out” during the summer.

‘Some mortality’ expected at GMF

Jody Bronson, a fourth- generation land manager and forester at Great Mountain Forest (GMF), said while he expects that “there will be some mortality” among the stands of red oak and other trees throughout GMF’s 6,000 acres of contiguous forest in Norfolk and Falls Village, he predicted that “once the gypsy moth completes its life cycle, the stands of oak should be OK.”

Many of the oak trees at GMF, he explained, are between 110 and 150 years old. “They have experienced gypsy moth infestations before. Last year we had record rainfall; therefore, the trees were not under stress,” he noted. However, Bronson said all bets are off on that optimistic outlook, “if the Northwest Corner goes into a drought situation this year, it could raise a concern.”

The fungus to the rescue?

As of mid-June, said DEEP’s Martin, it looks like there has been enough rainfall to halt the caterpillars’ feasting spree.

“It does appear that the fungus in the soil has activated. We were nervous that the rains weren’t going to be sufficient, but we’ve started seeing caterpillar mortality, which is super important, because they have to die before they pupate and lay eggs for 2023.”

He said all signs point to an end to the leaf-munching caterpillars by the end of June.

Spongy moth caterpillars feed on many species of trees and shrubs. Photo by Alexander Wilburn

Eileen Fielding, executive director of the Sharon Audubon Center, on Friday, June 17, stood next to a stately oak at the society’s entrance that for two years has been stripped of leaves by spongy moth caterpillars. Photo by John Coston

Spongy moth caterpillars feed on many species of trees and shrubs. Photo by Alexander Wilburn