CAPE ELIZABETH — Winter moths have been threatening the town’s population of deciduous trees since 2011, but the epidemic heightened this spring.
On Sept. 11, Tree Warden Todd Robbins presented the town with an understanding of the moths’ lifecycle, the risks they pose, and preventive measures the town and homeowners can take to reduce the risks.
Robbins, who is also the assistant property manager at Ram Island Farm for Sprague Corp., urged residents to monitor winter moth activity in town and on their properties and report their findings.
“I do want to talk to the residents that own these trees,” he said, “so we can make this area safe again.”
The winter moth is an invasive species, introduced to North America in the 1970s. The insect has been working its way through New England since the early 2000s. It feeds on the leaves of preferred hosts – oak, elm, maple, ash, and most fruit trees.
Unlike the browntail moth – whose microscopic hairs can cause itchy, irritated rashes to those who come in contact with them – the winter moth has no negative impact on human health.
According to Robbins, male moths are active from late November until January, as long as the temperature is above freezing.
“Some people claim that (the flight of male moths) look like falling snow,” Robbins said.
Female winter moths are flightless and can often be found at the base of trees. After mating, female moths deposit their eggs on host trees, where they remain throughout the winter, hatching in the spring when temperatures reach 55 degrees.
The larvae crawl up into leaf and flower buds and feed on the expanding buds and foliage. After the larvae have matured, they form cocoons in the soil at the base of trees where they stay from June until November.
Robbins said the spread of winter moths is increased by the spread of landscape materials, such as leaves and lawn clippings, as well of the transportation of vehicles and boats on which cocoons may have fallen.
Because there are no natural predators of winter moths in North America, their population is growing rapidly.
In 2013, the state introduced hundreds of parasitic flies in Harpswell and Cape Elizabeth – marked by the state as two of the most densely populated areas, where the threat of tree defoliation is high – in an attempt to decimate the winter moth. According to the Robbins, the parasitoid fly Cyzenis Albicans is from Europe and has kept winter moth populations there under control.
Robbins said there have been two releases of the flies at Two Lights State Park, but he estimated it takes seven to 10 years for the flies to affect moth populations.
“I’d like to encourage (more releases) to happen somewhere along the line,” Robbins said. “They live and die at the same life stages as the winter moth.”
Robbins said homeowners have several options for “integrated pest management.”
An early spray of trees with horticultural oil, purchased at landscape supply stores, may kill eggs before they hatch into larvae. Robbins said because the eggs are microscopic, it is difficult to reach all of them with the oils.
Tree companies can also be contracted to spray insecticides in the spring. But Robbins cautioned that insecticides don’t only kill the moths, but everything they touch.
Both of these options are most effective if scheduled before temperatures reach 50 degrees in the spring.
Systemic injection is a shot of insecticide into the bark of the tree that lasts multiple seasons and can be done at any time or temperature. However, if there is any rot in the tree, the injection will fail to spread, he said.
Another option is tree banding, which Robbins said should be done by Nov. 15, when adult moths are active. By applying a glue barrier to tree trunks, the wingless female moths are trapped. Tree bands can be purchased online and have been proven to minimize winter moth populations, but not eradicate them.
Robbins said he has ordered 500 feet of banding to use on town trees this fall. Each 250-foot roll costs about $800 to $850, including delivery. Robbins said 30-foot rolls can be purchased, but he is not sure how much they cost.
“Integrated pest management does not mean wiping something out,” Robbins said. “It means managing it … believe it or not, all insects are needed.”
He also stressed the importance of identifying and removing hazardous dead trees or limbs from public and private property.
In 2016, the town allocated $50,000 to help treat or remove trees damaged by winter moths.
“I have been with (Sprague) for 13 years, so I’m very familiar with the winter moth,” Robbins said. “I have taken down many trees that have succumbed to the winter moth epidemic.”
Female winter moths are flightless and can often be found crawling at the base of host trees where they lay their eggs.
Male winter moths are active from late November until January. Their flight is often explained as looking like falling snow.