Maine has a new pest that defoliates and has the potential to kill the state’s hardwood trees.

The winter moth has already established colonies in Harpswell and Vinalhaven, and could expand from those two coastal communities.

“The winter moth is a little inchworm caterpillar that is already causing a major problem in eastern Massachusetts,” said Charlene Donahue, a forest entomologist with the Maine Forest Service. “The infestation just started this spring in those two communities, and is centered in the populous parts of town. It has the potential of having a significant impact on the hardwood trees of Maine.” 

It also could affect food production because it attacks blueberries, cranberries and apple trees.

Donahue said the winter moth is originally from Europe, but she believes it arrived in Harpswell and Vinalhaven — communities with a large population of summer houses — when people from eastern Massachusetts dug up plants from their winter homes and brought them to Maine. With those plants came cocoons of the winter moth.

The moth’s first appearance in North America was in the 1930s, in Nova Scotia. In addition to Massachusetts, colonies have also been found in coastal British Columbia.

And while the moths have been found only in coastal locations, the eggs can survive really cold temperatures, so they could migrate inland.

Mainers are most likely to notice the winter moth in November and December, when the males congregate around outside lights when the lights are turned on after dark. The moths are light brown to tan, and have four fringed wings.

Females are flightless, with very small wings, and gray. They emit a sex pheromone that attracts the males for mating. The females then climb up hardwood trees, lay their eggs and die. The eggs will hatch in spring, producing the inchworm caterpillars.

Donahue said the residents of both Vinalhaven and Harpswell have been wonderful to work with, and have stopped giving any plants to people outside their area.

Cyndy Bush, president of the Harpswell Garden Club, said she and other people interested in fighting the winter moth will be holding informational meetings about the problem from 6 to 8 p.m. every Monday in October at the Harpswell Land Trust building on Route 123.

Bush said the winter moth has been confirmed only in the 400 acres on Harpswell Neck along Route 123, but that Jeff Gillis of WellTree plans to band trees in other neighborhoods where he thinks there might be some populations.

Donahue said conventional wisdom says that a hardwood tree can die after being defoliated three or four years in a row. Practically, however, it could take longer to eliminate trees in an infected area because the same trees are not likely to be defoliated every year.

And, she said, there are things that homeowners can do to control the winter moth, even though those efforts will not eliminate the problem.

“They can try banding the trees in their yard,” she said. By putting sticky bands around the trees, the flightless females climbing the trunks will get stuck and be unable to lay their eggs.

There are a few problems with banding, though.

“If the count gets too high and the band gets loaded with moths, other moths can just walk over them,” Donahue said. “And the eggs that get laid on forest trees can balloon on silk (sort of like a parachute) and re-infest trees that are banded.”

Bush said her group will be selling banding kits at its Monday meetings and also showing people how they can make their own bands with duct tape and Tanglefoot.

In the spring, Donahue said, people can use horticultural oil on hardwoods, suffocating the eggs so they don’t hatch.

Donahue said state officials don’t recommend chemical spraying to kill the moths, especially on Harpswell Neck, because it is a sensitive environmental area with a lot of lobstering. She said Bt, an organic treatment, works on young larvae, but not on older ones.

“There are biological controls,” Donahue said. “There is one that has been used very effectively, first in Nova Scotia in the 1960s and ’70s. It’s a parasitic fly, and they have not had a winter moth problem there since.”

The parasitic fly has also been used effectively in British Columbia, and has been introduced in Massachusetts.

Donahue said the U.S. Department of Agriculture, the U.S. Forest Service, the University of Massachusetts and the University of Maine have all agreed to work together on the Maine winter moth problem.

Some of the parasitic flies will be released in Harpswell next spring and, Donahue hopes, in Vinalhaven the spring after that.

“It is not an immediate solution, and not enough to eliminate the winter moth, but they are making an impact on the population elsewhere,” she said.

Donahue said the Maine Forest Service will be doing surveys in other parts of the state to see if winter moths are appearing elsewhere.

If people see a lot of moths flying around outside lights in November or December, they should contact her at 287-3244 or charlene.donahue@ maine.gov. They also can contact other offices, such as the Pest Management Office in Orono, because they all share information.

And people can contact Bush about the Harpswell efforts at bushcyndy@aol.com.

There is a catch, however. Maine has a native moth, closely related to the winter moth, called the Bruce spanworm that also flies in October and November. And the spanworm has been increasing in population recently.

So, while the moths you see in November might not be the ones that are the big concern, Donahue wants people to notify them anyway so they do not miss any winter-moth populations.

Tom Atwell has been writing the Maine Gardener column since 2004. He is a freelance writer gardening in Cape Elizabeth and can be contacted at 767-2297 or at:

tomatwell@me.com