What is it?
The yellowheaded spruce sawfly (Pikonema alaskensis) is native to North America. Mature larvae are about 20 mm (three quarters of an inch) long. They look like hairless green caterpillars with a series of darker stripes running along the body. They have a distinctive dark yellowish head.
What's the problem?
This pest attacks spruce trees, especially young, open-grown trees. The larvae eat all the new needles before moving onto older ones. Feeding damage starts near the top of a tree and moves downward.
This stripping of the needles can seriously weaken a tree. Moderate attack two or three years in a row can kill a spruce tree.
What can I do?
If the spruce trees attacked are small and few in number, this pest can be controlled by hand picking and destroying the larvae when they first appear mid to late June. Young larvae may also be controlled by hosing them off with a strong jet of water.
Unfortunately, damage to spruce trees is generally not noticed by homeowners until later when the larvae are quite large and have already started eating entire needles. These insects can be difficult to spot among the needles so careful, timely inspections are required.
Insecticide can be applied mid to late June to protect larger spruce trees under attack.