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DescriptionYellow-headed Spruce Sawfly

Yellowheaded spruce sawfly (Pikonema alaskensis) larvae grow to approximately 18 mm long, with mottled yellow to reddish brown heads. The body is yellow-green with six gray-green longitudinal stripes.

The adult is a stingless wasp. The female has serrated teeth not unlike those of a wood saw. The adults are a straw yellow with varying degrees of black markings on the head, from a few spots to totally black. The thorax has varying degrees of black markings.

Plants Affected

This is the most damaging of the five species of sawfly larva that feed on prairie spruce populations. They prefer open grown trees and will attack white, blue, black and Norway spruce.  This pest is favoured by dry conditions and has been at outbreak levels in Grande Prairie since 2008. 

Symptoms

Young larvae cannot chew cleanly through needles, so symptoms first appear as fallen red needles, as seen below.  Later instars are large enough to defoliate the new growth entirely, leaving only a few partial needles behind. This pest prefers to feed on new needles after they flush in spring.  Multiple years of infestation will give the tree a red tinge, as seen in the picture to the right.  Young trees may die after several successive years of infestation.

Control

Control may be achieved by hand picking and squishing larva in mid to late June.  In outbreak situations, spraying with an insecticide may be required to prevent heavy feeding damage, especially on taller trees.  Check with your local garden centre for insecticide options. 

Yellow-headed Spruce Sawfly     Yellow-headed Spruce Sawfly Larvae

Last updated: 9/13/2013 2:41:40 PM