What are spruce budworms?

Spruce budworms are insects that are native to North America. They are the most destructive pest of balsam fir, white spruce and black spruce.

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Adult Larva

What do spruce budworms look like?

The adults are usually dull gray with bands and brown spots. The hind wings are light gray with a wingspan of 20 millimetres.

The larvae are 18 to 24 millimetres long and cylindrical in shape. They have black heads and greenish-brown bodies. Their bodies are lighter on the sides with two rows of whitish spots along the back.

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What is the life cycle of a spruce budworm?

Adult moths emerge in late June or July and lay eggs in clusters on the needles. The eggs hatch into larvae in ten days. The larvae move to the crowns interior, seeking a favourable site to spend the winter. Here the larva spins a shelter within silken webs and becomes dormant. In May of the following year, the larvae emerge and feed on old needles, unopened buds or male flowers, until they make their way into the expanding candles. In June they pupate and then emerge as adult in late June or early July and the cycle repeats.

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What does spruce budworm damage look like?

Spruce budworms tend to be wasteful feeders. They bite needles off at the base and leave them hanging in a mass of silk. This causes masses of dried, red-brown needles hanging from the ends of the branches. They usually web two or three shoots together forming a feeding tube. Often during periods of high infestations, they eat all the new candles early in the season.

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Will spruce budworm kill my tree?

Losing a single year’s needles does not normally harm the tree. However repeated loss over consecutive years may cause the tree to die.

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How can I control spruce budworms?

When spruce budworm numbers are low, a strong stream of water can dislodge many larvae. Also, you can control them by hand picking from small trees. Environmentally friendly products can be used to control outbreaks  the active ingredient of these products being Bacillus thuringiensis var.kurstaki (Btk) or if desired a chemical control product, such as Malathion®, can also be used. Whenever you use an insecticide, always follow label directions.  Apply the insecticides just after the buds or candles have fully opened.

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