One of the best ways to confirm whether or not you have spruce budworms in your trees is to submit a report, including a description of the situation and a high resolution photo (larvae or moth, depending on time of year), to the Maine Forest Service Division of Forest Health & Monitoring. The report form can be accessed here.

Each fall, the Maine Forest Service and the Cooperative Forestry Research Unit (CFRU) at the University of Maine work with forestland owners around the state to collect sample branches from balsam fir trees for spruce budworm stage 2 larvae (SBW L2) analysis. These branches are chopped and washed in buckets, then residues are transferred to gridded filter paper discs where the SBW L2 are counted. The information garnered from these efforts provides information on spruce budworm population trends.

Unless landscape trees are under or next to older/taller spruce or fir trees, they are unlikely to sustain damage. Young trees that are in close proximity to spruce and fir may suffer from some defoliation, but are seldom killed. Spraying is effective protection if concerned. Trees older than 50-60 years are more vulnerable to defoliation damage. If budworm is detected, spraying is recommended for foliage protection.

The budworm is a wasteful feeder, chewing needles off at the base and webbing them to the tree. When the needles brown all at once, trees appear very unhealthy, but this may not be the case. Wait until later summer or early fall to evaluate tree health. Once brown needles are washed off by summer rains, green needles are easily seen. Trees with green canopy from the top down are still in pretty good shape. Trees with no needles on the canopy top are severely stressed. If the top turns white or silver, the tree most often dies.

The short answer is, we don’t know.  The likely answer is that it is normal.  In nature, population fluctuations happen.  There is a fairly long time-series of spruce budworm trap data from the pheromone traps and an even longer one from light traps.  In those data, we can see that the year-to-year catches do not make a smooth trend line when plotted over time.  Small fluctuations may be even more apparent in times when budworm populations are low.  We do have reports of other jurisdictions with similar results in 2016 despite using a different pheromone supplier, so the rumor that the pheromone did not work is not likely. 

Light trap catches were up compared to previous years—a look at the dates moths were caught reveals that many of those moths were trapped during the same time there was a large-scale migration event from the defoliated area in Quebec.  Canadian researchers looked at sex ratio from those flights, and found that 80% of the collected moths were female—those would not be attracted to pheromone traps, but may be lured by light traps.

For more information, see the 2016 Spruce Budworm Report from the Maine Forest Service.

The L2 survey is a data collection effort to determine spruce budworm populations. The “L2” is simply shorthand for “second instar larvae,” or the overwintering stage of the SBW. The SBW L2s are counted from branches sampled at a variety of plots throughout the working forests of Maine. In late fall (the collection period in Maine is generally late November through mid December), foresters collect 3 branches from each plot as well as record information on tree species, location, amount of defoliation (if any), and branch size. Samples are then bagged individually and taken to Spruce Budworm L2 lab at the University of Maine in Orono, to be processed. The L2 numbers revealed through this process provide forest managers with data showing trends for the area under study and help to forecast budworm density for the following year, which can be used to estimate defoliation level.  See our L2 Survey Maps for the latest survey results.

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It is not possible to have “experts” everywhere in the state, so volunteers who are willing to put up traps to help monitor the situation are invaluable. The Budworm Tracker Program is part of a large scientific initiative aimed at better understanding how spruce budworm populations rise and spread. As citizen scientists, they are asked to trap and collect spruce budworm moths during the moth flight season, between June and August, and send the data back to the research team. In Maine, the research team is particularly interested in recruiting volunteers in locations as far south as Bangor, north to the border with Québec and New Brunswick. Volunteers would be asked to check their traps once per week or even better, more than once per week, June through August. The traps are supplied for free and come with simple instructions. Individuals who are interested in becoming a citizen scientist can sign up by visiting www.budwormtracker.ca.

First thing to do is to assess the location, condition, and concentration of high-risk species in your stand to prepare an action plan to salvage or pre-salvage trees that will likely be lost through SBW mortality. Getting ahead of the outbreak in planning makes the most silvicultural and economical sense.

In general, all insecticides are registered and approved safe for use by Maine Board of Pesticides Control. Three intervention efforts that are most likely to be used for an outbreak in Maine are:

Btk is a naturally occurring soil bacteria and is not harmful to humans or other mammals, bees, birds, or fish when used according to label conditions.

Pheromones occur naturally, they are unique to each insect, and they trigger behavioral changes in members of the same species. Pheromones pose no risk to humans or other animals. They are used to lure or attract insects to traps, and they can be used to disrupt mating cycles. Spruce budworm pheromones do not kill insects.

Mimic (active ingredient is tebufenozide) is an insect growth regulator that larvae eat.  Mimic imitates a natural insect hormone that causes the developing caterpillars to molt prematurely as the larvae go through their growth stages. The caterpillars then quickly stop feeding and die. It is harmless to humans or other mammals, bees, birds, or fish when used according to strict label conditions.

Although an infestation will not likely have a huge impact on the trees in southern Maine, the potential economic impact could be quite strong. Markets will directly impacted in the northern and western areas of the state will have a ripple effect in southern areas.

Because the spruce budworm outbreak will have a substantial impact on forest composition and structure over large areas, the next outbreak will likely have an influence on wildlife habitat over a long period of time. For example, mature spruce-fir stands are vital to deer wintering areas (DWA), so a decrease in DWA areas due to an SBW outbreak are likely to lead to higher winter mortality in deer (as well as impact other species associated with mature, softwood-dominated canopies such as Canada lynx). Although insecticide spraying for SBW will have little or no direct impact on lynx, snowshoe hare, or moose. That being said, snowshoe hare need cover from predators, which is best provided by regenerating young softwoods (15 to 40 years old). The interface between mature timber and regenerating softwood stands may facilitate the ability of Canada lynx to hunt snowshoe hares. On the plus side for moose, if areas are heavily salvage logged, the increased area of early successional habitat will increase available moose browse.