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Spruce Budworm in Maine
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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.
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 2025
In 2023, monitoring data suggested SBW populations were building toward an outbreak in northern Maine. When reports of visible damage began in 2024, MFS conducted an aerial survey and recorded roughly 3,400 acres of damage in northwestern Maine. During the winter, the University of Maine Spruce Budworm lab monitored SBW larvae (L2) on tree branch samples and found populations that were at or above the action threshold of an average seven larvae per branch in northern Maine. When larval populations are at or above the action threshold, an outbreak of SBW is likely to occur.
With the increase of SBW in these areas, timberland owners and managers in Maine formed the Maine Budworm Response Coalition (MBRC) and are working collaboratively with the MFS, Cooperative Forest Research Unit, and Maine Forest Products Council to reduce impacts from SBW as it builds toward outbreak conditions. The coalition successfully advocated for emergency funding to implement Early Intervention Strategy (EIS), a method developed and tested in New Brunswick, Canada to reduce SBW populations below the outbreak threshold. When SBW populations are reduced, natural enemies and other mortality factors can keep SBW populations from erupting. To be most effective, this strategy will need to be implemented at the landscape scale and across all ownerships before an outbreak occurs.
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 is collaborating with the Maine Forest Service (MFS), who will provide technical assistance and communications with landowners and the public regarding biology, management options, and SBW history. Additionally, the MFS will provide financial oversight and reimbursement for the state and federal funds supporting the SBW response.
Eastern Spruce Budworm Early Intervention Strategy Cost Share Program Application Guidelines (PDF)
MFS is working with landowners, scientists, the University of Maine, and other agencies to inform the MBRC where treatment is needed and how to best target those areas to reduce SBW populations below the outbreak threshold. To achieve this goal, the MBRC will be coordinating the administration of low-toxicity insecticides through an aerial spray program in late May through early June 2025. Roughly 240,000 acres in northern Maine with larval populations at or exceeding the outbreak threshold will be targeted.
In 2025, the MBRC is planning aerial applications for two operational areas: (1) general location of Cross Lake and the surrounding Fish River Chain of Lakes, and (2) lands along the Quebec border, stretching from Estcourt and St. Pamphile easterly towards the St. John River.
- Aerial spraying will only be applied:
- Inside predetermined areas of spruce-fir forest with SBW populations that are at or above the action threshold
- No closer than 100 ft from lakes, streams, other bodies of water and ¼ mile from identified habitat of state endangered and threatened butterflies
- In good weather (no rain or high winds) to prevent drift or unintended applications
- Using reduced-risk insecticides that only affect larvae that eat treated foliage
Insecticides containing active ingredients tebufenozide (Mimic) or Btk (Bacillus thuringiensis kurstaki, Foray) will be 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.
Publicly shared maps of planned treatment areas will be available soon. To protect the public, road access in these areas will be temporarily blocked during active spray operations and until the spray application has dried – you may encounter roadblocks with the following signage. Please do not enter areas sooner than 4 hours after application.
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.
- 2024 Pheromone Trap Map
- 2024 Ground Defoliation Survey
- Larval Populations (L2) Map
- Pheromone Trap Maps
- Annual Reports
Upcoming Events
Spruce Budworm Informational Session
When: May 1, 2025, 1-4PM
Where: Wells Conference Center, University of Maine Orono (131 Munson Rd, Orono)
AND University of Maine Fort Kent (23 University Drive, Fort Kent)
AND Virtually via Zoom
In collaboration with the Maine Forest Service, Cooperative Forestry Research Unit, and the Spruce Budworm Task Force, Keeping Maine's Forests is hosting a free hybrid informational session with presentations about Maine's building spruce budworm populations and the early intervention strategies being used to prevent an outbreak. There will be an opportunity after the presentations to ask questions directly with the experts. Maines forestry community is diverse and interconnected - whether you are an interested member of the public who lives, works, or recreates in the Maine woods, this event may be for you. All are welcome. Registration is required.