On Colorado blue and Norway spruce trees, green or purplish shaped growths (galls) up to 2 inches long appear on the tip of branches of trees. The galls turn brown as the summer progresses and are very noticeable by fall. The galls are generally not life threatening to the trees, however, in large numbers, they can become quite unsightly.

On Douglas fir trees, white, cottony tufts appear on the undersides of needles in midsummer. Small, (1/8 inch) blackish insects may be found under the tufts. Needles are spotted yellow and may be distorted.

 These growths are caused by an insect called the Cooley spruce gall aphid. In the late spring, it feeds, matures and then lays eggs at the base of needles near the tip of the branch of spruce trees. When the eggs hatch, the young insects move to growing needles and begin to suck the juices from them. This damage stimulates the plant to form the galls.

The aphids live and feed inside the chambers of the gall until about July when the mature insects emerge. They develop wings and fly to a Douglas fir or another spruce tree. On the Douglas fir, the aphids lay eggs and produce a generation of woolly aphids. Some of these aphids develop wings and fly back to the spruce to start the cycle all over again the next spring.

 On small spruce trees or where practical, cut off the galls as they are developing in the early summer.

To prevent establishment of the galls on spruce, spray with an insecticide labeled for this problem in the spring as the new buds at the tip of the branch are elongating.

On Douglas fir, spray with an insecticide labeled for Cooley spruce gall when the new growth is expanding to control hatching insects.

Commercial spray companies may soil inject a product called Merit in the fall for control of spruce gall aphids (adelgids).

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

 

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