Take a quick scan of the new growth on spruce, especially Colorado spruce (Picea pungens). Look for straw-like needles that are withering….and the disappearance of needles all together. This is very typical damage of Yellow Headed Spruce Sawfly (Pikonema alaskensis).
And here is the little beast, they really blend in to the foliage and they are easy to miss.
As they get larger, the head and body darken. Spruce sawfly larvae can grow to be 2 cm long.
And boy can they eat! This is typical yellow headed spruce sawfly injury on our beloved Colorado spruce. We also see them on white spruce.
Management of the larvae includes insecticides such as Pounce (permethrin), Success (spinosad) and others. Larvae can be found on new growth, making coverage and management a little more achievable. Pounce is photo-sensitive, try applying on cloudy days or late evening.