Spruce Budworm & Balsam Fir

This is a Balsam Fir that killed by Spruce Budworm (Choristoneura fumiferana) about 30 years ago. This picture was taken in North Mountain, CB, March 2010.

While at North Mountain, located in the Cape Breton Highlands, we observed some Balsam Fir that had been destroyed 30 years previous by the spruce budworm (Choristoneura fumiferana). Now you might look at the picture taken and think this spruce budworm outbreak back in the 1970’s was terrible news for Balsam Fir and it was, but it was also part of this Balsam Fir’s life cycle. You might be interested to know that spruce budworm outbreaks occur periodically and frequently enough that they are considered part of the natural cycle of the maturing of Balsam Fir. Spruce budworm outbreaks occur on average every 35 years so since the last outbreak reached its peak in Nova Scotia 1976 we are due for another outbreak in the next few years.

Spruce budworm is an extremely destructive native insect which affects Balsam Fir stands in Cape Breton significantly. Balsam fir, well known for its attractive features as a conifer, is marred by spruce budworm outbreaks.

Spruce budworm usually lay their eggs on the under surfaces of needles of the host tree where the larvae will overwinter. In the spring when buds begin to swell, the larvae emerge from their silk shelter “hibernacula” and start feeding on needles and buds. Newly hatched budworm larvae bores into the needles and expanding buds of Balsam Fir and feeds. The needles are then severed and turn brown giving affected Balsam Fir’s a burnt or scorched appearance. If spruce budworm populations are high, significant damage can be caused. Since they eat the Balsam Fir foliage, the tree cannot photosynthesize and without this vital energy source, it dies. During spruce budworm outbreaks the larvae can destroy all of the new foliage and they sometimes feed on the buds and shoots resulting in the Balsam Fir becoming stunted, dead, or have dead tops. Not all affected Balsam Fir die during a budworm outbreak. Many survive the outbreak and can regenerate enough to only become damaged or marred. After more than a year of heavy defoliation, individual trees begin to die.

Although Balsam Fir is most frequently affected, other trees can be killed when spruce budworm populations are high. Other suitable hosts include spruce, Tamarack, pine and Eastern Hemlock.

Natural factors such as adverse weather, disease, predators, and parasites help keep budworm populations under control. Heavy outbreaks of spruce budworm may be attributed to favourable weather, adequate food sources, and suitable overwintering sites for the larvae. These budworm aren’t all bad either - some species such as woodpeckers and nuthatches actually benefit from the Spruce Budworms effect on forests.