Cooley Spruce Gall Adelgid
Cooley spruce gall adelgid infestation (Petr Kapitola, Central Institute for Supervising and Testing in Agriculture, Bugwood.org)
- small; early stages may be 1/20 inch long
- aphid-like appearance
- produce white, cottony egg masses on spruce twigs
- most visible inside of 2–3 inch pinecone-looking galls
- galls are green in the spring and turn brown in summer
Host Plants, Diet & Damage
- spruce (primary host) and Douglas-fir (alternate host)
- feed on plant sap; cause large, 2–3 inch long galls on spruce
- stipple and bend needles on Douglas-fir
- damage primarily aesthetic
- damage is rarely a threat to tree health
Biology, Life Cycle & Damaging Life Stage
- overwinter as adult females or nymphs on spruce bark or beneath spruce buds
- in spring, eggs are laid near new buds and hatch around budbreak
- nymphs feed on sap at the base of needles, forming galls
- galls protect insects from foliar pesticide applications
- in mid-summer, nymphs exit galls and fly to Douglas-fir
- multiple generations occur on Douglas-fir before some adelgids return to spruce
- some adelgids overwinter on Douglas-fir
- The Cooley spruce gall adelgid has little negative effect on tree health; tolerate pest.
- Some spruce trees are more resistant than others.
- Do not plant spruce and Douglas-fir close together.
- Apply horticultural oil before budbreak (warning: oils may discolor spruce needles).
- Apply cover spray (carbamate or pyrethroid) before budbreak.
- Apply a systemic insecticide (neonicitinoid) in the spring.