CUMBERLAND — Town officials have modified their plan to spray insecticide to fight a browntail moth infestation, in response to residents’ concerns about environmental threats posed by chemical pesticides.

The town proposed using a truck-mounted sprayer to coat trees along three miles of Foreside Road with a chemical insecticide to kill browntail moth caterpillars. The invasive insects defoliate trees and can shed tiny hairs that cause skin rashes and respiratory problems in some people.

Although many residents support using pesticides to curb the worst moth infestation in more than a decade, some worried that a synthetic insecticide could harm people and the environment, including marine life in Casco Bay.

Terry Traver, a licensed pesticide applicator with Whitney Tree Service, said the town decided instead to use a naturally derived pesticide to tackle the infestation.

“We feel like it is a more environmentally friendly approach with some of the residents who were concerned about spraying pesticides, with their gardens and pets,” Traver said.

The natural treatment could be less effective than a synthetic spray, but it is less harmful to the environment, he said.

Browntail moths nest high in oak and apple trees. In May, 2-inch-long caterpillars break out of the nests and start feeding on new leaves before spinning cocoons in late June to pupate into moths.

The caterpillars can do extensive damage to trees and are covered with toxic hairs that can drift through the air and cause a rash similar to poison ivy and provoke respiratory problems for some people. The moths shed their skins five times a season, and the hairs stay in the environment and can cause problems for months after the caterpillars are gone.

Ivy Frignoca, the bay keeper for Friends of Casco Bay, said her office received half a dozen calls from residents with concerns about the spraying program before a public meeting on the proposal last week. Concerns about damage ranged from people and pets to marine animals along the coast.

“As the lead advocate for Casco Bay, when an issue like this comes up that threatens the health of the bay, we have to look into it,” Frignoca said.

The town planned to use Tempo, a synthetic neurotoxin, to kill the caterpillars. Tempo is extremely toxic to fish and aquatic invertebrates and should not be allowed to run into storm water, according to the warning documents for the treatment. Even though state rules prohibit spraying pesticides within 250 feet of any shoreline, people were concerned that the chemical could find its way into Casco Bay and harm shellfish.

During the last browntail moth infestation, in the late 1990s, communities around Casco Bay used aerial sprays to counter the insects, but that was controversial because of its negative effect on shellfish, particularly lobsters. Cumberland is not considering an aerial spraying program this year.

For the spraying to be effective, the town needs a majority of Foreside Road residents to sign consent forms allowing the town’s contractor to spray on their properties. The deadline for signing the forms is Friday, and the town intends to start spraying next week.

Town Councilor Tom Gruber, a Foreside resident, said in response to resident concerns that the council decided to spray with spinosad, a chemical derived from soil bacterium that is toxic to insects and sold under the brand Conserve SC. The pesticide is less harmful to shellfish and it sticks to soil, giving it less potential to move to groundwater.

The town planned to spray only along Foreside Road, but now is expanding the scope of the project to include 18 private side streets. Private roads will be charged $300 to $500 for treatment, depending on the length of the road, according to a letter to residents from Town Manager Bill Shane.

The cost of the natural treatment is expected to be slightly more than the synthetic chemical, but Gruber said it shouldn’t exceed the $15,000 budgeted for the project.

“After a long discussion and concerns, we came up with a more environmentally friendly plan,” Gruber said.

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