The feeding of these adelgids on the tender stems of spruce and fir causes deformed sections, similar in appearance to cones or pineapples, which distort the stems and stunt the growth, usually girdling the stem at that point. A continuing infestation on a tree will seriously disfigure it, weaken it, and make it more susceptible to attack by other insect pests. Immature aphids overwinter in crevices in the bark of the tree, and in early spring mature to adults with wings. These now lay eggs on the new twigs, and these new nymphs begin feeding near the base of new buds, causing the tissues at that point to swell and form the gall, inside which the nymphs continue feeding, now protected by the gall. This generation matures, emerges as winged adults in late summer which may migrate to new host trees, lay eggs, and the resulting nymphs from these eggs overwinter for the next year.
On small trees physical removal of the galls early in the summer will be helpful, but on larger trees is impractical. Dormant oil applications to the trunks and stems of the trees in late winter will smother over-wintering nymphs, with care NOT to spray the foliage of blue spruce, as the oil will discolor the tree. Contact insecticides can be applied to coincide with emergence of new nymphs at about the time new buds are forming on the tree. Once galls have formed the insects will not be affected by pesticides. A fall application of a contact insecticide, to the trunks and stems, will be effective in killing nymphs that have moved into crevices for the winter.