COOLEY SPRUCE GALL ADELGID ( Adelges
cooleyi )
The Cooley spruce
gall adelgid, causes unsightly cone-like
galls on Colorado blue spruce and bending and spotting of Douglas-fir needles.
Sitka and Engelmann spruce may also be attacked by this pest. Immature female
insects overwinter near terminal buds on the underside of spruce shoots,
and on the undersides of the needles of Douglas-fir.
In the spring, the females (stem mothers) begin to mature, produce a waxy
covering and may lay up to 100 eggs. Eggs require only 7-10 days to hatch,
and appear to be well-timed to coincide with tree development as hatching
generally begins right around the time the trees are breaking bud. The nymphs
on spruce crawl to the base of needles on the nearest newly developing shoot
and begin to feed, and their feeding causes the shoot to grow in such a way
as to enclose the nymphs within the gall as it forms. Later in the summer,
the galls will dry and crack open, and mature adelgids emerge to molt and
develop wings, and lay more eggs on other spruce or Douglas-fir. When the
eggs hatch on Douglas-fir, the nymphs crawl to tender growth and begin feeding
on the undersides of the needles causing discoloration and bending of the
needles.
Fig. 1. The tiny dark specks visible on this newly emerging growth (especially
near the base of the shoot) are the recently hatched crawlers on Douglas-fir.
The Cooley adelgid thrives where it can alternate generations between
hosts, so keeping Douglas-fir and blue spruce separate may help to weaken
the life cycle. Chemical controls are available. Control on blue spruce is
best accomplished in the spring when adelgids first become active. If the
population is small, picking galls off before July 1st and destroying them
may be another viable alternative. On Douglas-fir, you may treat during dormancy
or when the crawlers are visible.
Return to Pest Menu