Spruce Gall Adelgid
Article by: Afton Pick
Cooley spruce gall in action.
Cooley spruce gall adelgid (Adelges cooleyi) is a species of adelges, closely related to aphids, that produces galls on the end of the new shoots. The species alternates between white spruce and douglas fir. The insects are difficult to see and they will most likely be noticed by their damage. This insect requires 2 years to complete its full life cycle.
In the spring on white spruce overwintering nymphs, immature adelgids develop into wingless females. When they mature they begin laying eggs at the branch node. After laying the eggs, the mother creates a cottony, protective covering for them. After a couple weeks, nymphs emerge from the eggs and the mother begins sucking sap at the base of the needles. This causes the gall, an enlarged growth, to form around the nymphs.
The galls are cone-like structures that are pineapple-shaped. They start out light green in color, and then swell and turn pink or brown. The nymphs mature inside the galls and emerge in mid to late summer, with some becoming winged adults. The winged adults then fly to douglas fir trees where they lay eggs on the needles and cover them again in a cottony, protective covering.
Young nymphs emerge in late summer and overwinter at the base of needles. In early spring the young nymphs start feeding again, but this time, no galls are formed. In the end of summer the winged adults fly back to the white spruce.
In areas like Saskatchewan, where douglas fir is not available, they can complete the entire two year life cycle on white spruce.Damage caused by the cooley spruce gall adelgid is not really a problem in the forest industry, but can cause aesthetic problems in ornamental plantings and Christmas tree plantations. It results in death of new growth. Years of damage can result in an unsightly tree, but will not kill your tree.
To control this issue, and if you only have a few galls, prune them off before they open and the adults emerge in July. If you have a large infestation, spray the plant with insecticidal soap in early spring when the new growth is starting to form. You could also apply a dormant oil over the whole plant in late winter before new growth begins, which would kill the overwintering adelgids. If you are planning on using a dormant oil take caution that some species may be sensitive to this spray. Always read chemical labels before applications. You can even test spray a branch and see how it reacts before spraying the whole plant.