Spruce budworm population remains contained

Posted on February 21 2019

By Rob Johns, forest insect ecologist, Canadian Forest Service, NRCAN

The latest spruce budworm outbreak emerged in Quebec in 2006 and has since expanded to cover more than 8 million hectares. In 2014, budworm populations began rising in New Brunswick and scientists began testing and implementing the Early Intervention Strategy (EIS) as a way to contain the outbreak to northern New Brunswick.

In a nutshell, the research involves intense population monitoring followed by targeting and treating hotspots at the leading outbreak edge to prevent further spread. Leading this initiative is the Healthy Forest Partnership, a group of scientists, academia, government, and industry working together to find new ways to limit spruce budworm’s impact in Atlantic Canada.

Population monitoring indicates a ~90% projected decline in hotspots or treatment areas in New Brunswick from last year, even as the outbreak in Quebec continued to expand. This marks the first spruce budworm decline in New Brunswick since the research began in 2014. While the exact causes of decline remain under study, this substantial decline in budworm offers strong support for the effectiveness of the Early Intervention Strategy.  

This year’s decline in spruce budworm populations is significant for several reasons, but should be interpreted with caution.

On the plus side, the reduced number of budworm hotspots will result in a substantial decline in the area to be treated in 2019. The exact areas and locations of treatments for 2019 will be determined in the early spring.

Moreover, less budworm in 2019 means that trees will get a year of reprieve from defoliation and will thus have an opportunity to grow new foliage and recover the loss from the past couple of years. Remember, it usually takes 4-5 years of severe and sustained defoliation to kill balsam firs and spruce trees, so even a year of relief can be significant for reducing growth loss and mortality.

Perhaps most importantly, the contraction of the outbreak area in New Brunswick means fewer potential sources of budworm moths that might seed further outbreak spread through New Brunswick and into other Atlantic provinces and Maine, USA.

Now for a note of caution. Peaks and valleys in budworm populations from year to year is not uncommon and have been recorded in previous outbreaks.  Although results are reassuring this year, management efforts for spruce budworm are not over. Just to the north of the New Brunswick border is a thriving and still expanding outbreak of spruce budworm. Under the right conditions, we could see another mass inflight of moths from Quebec that could help repopulate northern New Brunswick, similar to what occurred in July of 2016 in the Campbellton/Dalhousie area. What the past few years has taught us is that we can effectively manage these occasional influxes of budworm moths with the Early Intervention Strategy. However, even with a well-operating Early Intervention Strategy, we should anticipate periodic hotspot spikes and declines in New Brunswick to continue for as long as the broader outbreak is underway. 

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