Spruce Budworm in Maine

Spruce budworm (Choristoneura fumiferana)

Spruce budworm (SBW) populations are increasing in Northern Maine. The Maine Forest Service (MFS) is a member of the Spruce Budworm Task Force (SBWTF) and with collective input based on the research conducted under the Healthy Forests Canada and others, the Spruce Budworm Task Force determined that the Early Intervention Strategies (EIS) shown to be successful in New Brunswick would be the best strategy for the protection and health of Maine’s forests.

Spruce budworm larva and adult moth
Image: (Left) A spruce budworm larva. (Right) An adult spruce budworm moth next to a spruce budworm pupa. Spruce budworm moths are variable in color but always have a black bar on both their wings. Credit: USDA Forest Service, Budwood.org.

General Information

Spruce budworm (SBW) is a native moth that defoliates balsam fir and spruce trees during the larval (caterpillar) phase. SBW is capable of widespread outbreaks that can cause extensive damage and mortality to spruce-fir forests after several years of feeding. SBW populations are normally present in Maine’s forests, but outbreaks can occur roughly every 40 years.

In Maine, the last SBW outbreak happened in the 1970s-1980s, where close to seven million acres of spruce and fir suffered severe damage and mortality. As a result, many trees that were dying from SBW damage were salvaged by clearcutting, a logging practice that involved cutting down most or all the trees in an area, which changed the forest landscape for the Pine Tree State for years. In addition to reduced natural resources and diminished water quality, local employment for those who rely on Maine’s forest-based economy was also impacted. Dead and dying trees provided fuel for wildfires to spread, which also reduced Maine’s air quality and resulted in drastic changes to wildlife habitat.

SPRUCE BUDWORM IN MAINE:
MODERATE OR GREATER DEFOLIATION
1918-1988

Spruce Budworm in Maine, 1918 - 1988

Spruce Budworm in 2026

The first step in understanding where spruce budworm populations are building is through intensive survey and monitoring. One way this is accomplished is through collecting branch samples from fir and spruce trees. During the winter, the University of Maine Spruce Budworm lab processes these branch samples and counts the number of overwintering spruce budworm larvae, otherwise known as “L2”. Those locations with more than seven L2 per sample have budworm populations growing beyond what natural enemies can help control. When larval populations are at or above this action threshold, an outbreak of SBW is likely to occur.

Spruce budworm is also monitored through Maine Forest Service aerial surveys. In 2024, roughly 3,400 acres of damage was recorded in northwestern Maine. Following the reports of damage and elevated L2 counts in these areas, the Maine Budworm Response Coalition (MBRC) implemented an Early Intervention Strategy (EIS) to protect Maine’s forests before spruce budworm populations were expected to outbreak, or in some cases, prevent the spread of an active outbreak. Read more about the EIS efforts in 2025 in “Aerial Spray Program 2025”.

An aerial view of defoliation from spruce budworm in July 2024 in the T18R13 WELS region (Aroostook County). The reddish-brown color of the spruce and fir trees, an indication of spruce budworm feeding.
Image: An aerial view of defoliation from spruce budworm in July 2024 in the T18R13 WELS region (Aroostook County). Note the reddish-brown color of the spruce and fir trees, an indication of spruce budworm feeding.

During aerial surveys in 2025, no visible damage was seen in the northwestern portion of the state where EIS treatments occurred. However, in untreated areas in the northeastern area, 3,900 acres of damage from spruce budworm was documented.

Early Intervention Strategy in 2026

In 2025, the Maine Budworm Response Coalition (MBRC) worked collaboratively with the Maine Forest Service to implement an Early Intervention Strategy (EIS) to reduce the rising spruce budworm populations, protect the health of our forest ecosystems and resources, maintain wildlife habitat, and prevent impacts to our forest-based economy.

To read more about last year’s efforts, please read “Aerial Spray Program 2025”.

The main goal of Early Intervention Strategy is to help maintain healthy trees by using targeted insecticides to reduce building spruce budworm populations early – when they are still low – instead of waiting until populations have already exploded. Any spruce budworm management across the landscape is a multi-year effort, and an EIS approach is no exception. That said, because EIS focuses on reducing spruce budworm populations before they outbreak, EIS can drastically reduce the amount of acres affected and subsequently reduce the cost of management in the long term.

Following the success of targeted management last year, managers have opted to apply EIS in 2026 to suppress elevated populations of spruce budworm. After monitoring and L2 surveys during winter 2025-2026, roughly 83,000 acres have been identified as hot spots – a significant decrease in acres that could be managed compared to the documented acres of hot spots the year before. Approximately 70,000 acres of forest have been identified for potential treatments in late May and early June 2026.

To offer small Maine landowners an opportunity to participate in the success of EIS, the Maine Forest Service created a small landowner program to set up cost-share treatments in 2026. We are not currently accepting additional landowners for this program, but there may be additional opportunities to participate in EIS in 2027.

Additional details of the EIS treatments in 2026 will be available here and on the Spruce Budworm Task Force website.

See the success of the 2025 EIS treatments:

After targeted aerial applications in 2025, winter L2 surveys revealed a ~95% decrease in spruce budworm populations in treated areas, while untreated sites experienced an expected increase. Untreated acres in 2025 were primarily in small ownerships, an opportunity to participate in the program was advertised to small landowners from July through November 2025 and a portion of those acres will receive EIS treatments in 2026.

Early Intervention Strategy - Before Aerial Application

A map displaying the final 2024-2025 forecast of spruce budworm populations for the basis of the 2025 Early Intervention Strategy.



Early Intervention Strategy - Aerial Application

A map displaying the 2025 Early Intervention Strategy.



Early Intervention Strategy - After Aerial Application

A map displaying the 2025-2026 forecast of spruce budworm populations for the basis of the 2026 Early Intervention Strategy.

Aerial Spray Program 2025

The Maine Budworm Response Coalition (MBRC), comprised of timberland owners and managers in Maine, successfully advocated for emergency funding to oversee and implement the Early Intervention Strategy (EIS) methods to reduce the rising SBW populations and protect the health of our forest ecosystems and resources, maintain wildlife habitat, and prevent impacts to our forest-based economy. The MBRC collaborated with the Maine Forest Service (MFS), who provided technical assistance and communications with landowners and the public regarding biology, management options, and SBW history. Additionally, the MFS provided financial oversight and reimbursement for the state and federal funds supporting the SBW response. In 2025, $9.81 million of $12 million appropriated federal funds were provided for reimbursement of treatment costs. An additional $500,000 was contracted with the University of Maine L2 lab to support monitoring of SBW L2 populations. The remaining funds will be used to continue to support the EIS response in Maine.

MFS worked with landowners, scientists, the University of Maine, and other agencies to inform the MBRC where treatment was needed and how to best target those areas to reduce SBW populations below the outbreak threshold. The MBRC coordinated the administration of low-toxicity insecticides through an aerial spray program that concluded in early June 2025. Roughly 240,000 acres in northern Maine with larval populations at or exceeding the outbreak threshold were targeted. Additional details on the aerial treatments can be found on the Spruce Budworm Task Force page.

Insecticides containing active ingredients tebufenozide (Mimic) or Btk (Bacillus thuringiensis kurstaki, Foray) were applied by helicopter and/or fixed wing aircraft using modern technologies to ensure accurate applications. SBW populations may require additional aerial applications over the coming years to ensure the populations do not reach an outbreak level.

Monitoring Programs

A successful SBW monitoring program requires a multi-pronged approach and relies on the use of methods such as pheromone trapping, light trapping, overwintering larval (L2) sampling, and aerial and ground survey. Partnerships and observations from the community are key to a comprehensive monitoring program. MFS leads pheromone and light trapping and aerial and ground survey efforts. MFS supports the larval monitoring conducted by the University of Maine Spruce Budworm Lab.

Upcoming Events

Spruce Budworm Information session on Tuesday, March 24, 2026 at Nadeau Hall, University of Maine Fort Kent, Fort Kent Maine 04743

Spruce Budworm Informational Session

When: March 24, 2026; 6:00 - 7:00 PM
Where: Nadeau Hall, University of Maine Fort Kent, Fort Kent Maine 04743

Join us for an in-person presentation to learn and ask questions about spruce budworm biology & history, upcoming aerial applications planned in Fort Kent and surrounding areas this spring, and possible impacts for local community members, including temporary trail closures. This event is free and open to the public.