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.

Additional photos

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