Maine will move forward with an effort to control spruce budworm infestations near the Canadian border, but the failure to get emergency state funding will limit the acreage that can be sprayed with insecticide this spring.

The state has enough money to spray about 85% of the land on the verge of a spruce budworm outbreak.

The Maine Forest Service needed $15 million to fully fund its plan to spray aerial insecticide on about 303,000 acres of forest in the Saint John Valley and along the northwest border with Quebec to kill the caterpillars when they emerge from hibernation to feed on tree needles in late May and early June.

The agency had proposed a preventative spraying program modeled after New Brunswick’s successful early intervention effort that would be funded by a $12 million federal grant, $2 million in state funds and $1 million from commercial forest owners that suffer the most from a budworm outbreak.

But because of a breakdown in budget negotiations at the State House, Maine’s share of the program funding won’t be available until after the spraying window is closed. That is forcing the state to scale back its spraying program by about 40,000 acres, said Allison Kanoti, an entomologist with Maine Forest Service.

The funding was included in the $11.3 billion state budget that Gov. Janet Mills signed into law last week. But a supplemental budget failed to attract the two-thirds support of lawmakers needed to immediately take effect as an emergency measure. As a result, state funds won’t be available until June 20, which is too late for budworm spraying.

The Maine Forest Service estimates that $13 million can cover aerial spraying of 240,000 acres considered to be on the verge of a budworm outbreak. Forests with spruce and fir trees that have more than three overwintering larvae per branch are deemed at risk. Six or more per branch is considered a hotspot.

Spruce budworm is a native moth whose population explodes every 40 years or so, making it one of the most damaging forest pests in North America. Budworm caterpillars feed on the buds and needles of host spruce and fir trees, which, if left untreated for a few years, kills the trees.

The Maine Forest Service plans to use two insecticides to control the budworm: Tebufenozide, a $45-an-acre synthetic insecticide branded as Mimic that kills caterpillars by causing premature molting, and BtK, a $90-an-acre organic insecticide that kills caterpillars by destroying the gut after it is ingested.

Both are considered to be targeted insecticides that pose very low risk to humans, according to the state toxicologist, because they only affect lepidopteran species — the butterflies, moths and skippers of the insect world — and must be ingested, not just touched, to be effective.

If left untreated, budworm will kill one out of three spruce trees and five out of six fir trees, usually after about three years of defoliation. Those stands of dead trees pose a wildfire threat, degrade water quality and undermine wildlife habitat for a variety of species, ranging from boreal birds to cold-water fish.

The last Maine outbreak destroyed more than 7 million acres of forest. A 2016 legislative task force estimated a new outbreak could eliminate almost 3,800 jobs and cost Maine $794 million a year. Maine hopes to avoid a repeat of that ruin through an aggressive whack-a-mole management approach.

The state has expanded its ability to look for cocooning budworms before they emerge in the spring and begin to feed, giving landowners time to spray the infested stands with just enough pesticide to return a hot spot to non-threatening levels that can be kept in check by weather and natural predators, like birds.

New Brunswick has used this early intervention strategy to stop Quebec-based budworms at its borders. But the state estimates it will cost $15 million a year to do that, with no certainty about how long it will have to be done to keep the budworm at bay.

As the agency that will implement the response program, the Maine Forest Service is still deciding which areas it won’t spray. It knows it doesn’t have enough information to spray all of the Saint John Valley, Kanoti said. It is mapping out the location of houses, waterbodies, and sensitive wildlife habitats to avoid.

The state will prioritize secluded hotspots in large swaths of uninterrupted forests to maximize efficiency.

But the $2 million in state funds won’t go to waste, Kanoti said. The state has many years of budworm spraying ahead of it to try to contain the effects of the voracious defoliation. The $2 million from the budget will be set aside for next year’s spraying.