University of Illinois Extension

University of Illinois Extension

Hort Answers

Insect Damage

Spruce Gall Adelgids
Adelges cooleyi, Adelges abietis

2 (1 = rare 5 = annual)
2 (1 = very little damage 5 = plants killed)
The Cooley spruce gall adelgid (Adelges cooleyi) attacks Siika, Oriental, and Colorado blue spruce and Douglas fir. Eastern spruce gall adelgids (Adelges abietis) attacks mainly Norway spruce, but can be found on Colorado blue, white, and red spruces.

Plants Affected
The Cooley Spruce gall tends to go out to the tip of the shoot. The shoot may curve as a result of the gall being on only on side of the shoot. The entire new shoot may be one long gall too. On the spruce, galls are evident. On Douglas fir, there is no gall, but severe infestation does cause yellow spots to appear on the needles. Eastern spruce gall adelgid galls look like a tiny pineapple near the base of the shoot.

Life Cycle

With the Cooley Spruce gall adelgids, the immature female overwinters and maturesin the spring. She lays several hundred eggs on side branches. After the eggs hatch, the young migrate to the base of needles on the new growth. The feeding induces the plant to envelope the individual adelgids as a group, thus forming a gall. By late June to July, the adelgids emerge from the galls. The females become winged and fly to Douglas fir or other spruces. Several life cycles later, and through most of another growing season, the adelgids return to the spruce trees. It takes two full growing seasons for the adelgids to make one complete cycle between both hosts.

The Eastern spruce gall adelgids overwinter as immature females, the females mature in the spring and lay between 100 and 200 eggs next to buds ready to open. The young feed on needles and eventually move to the base of the needles. A gall develops. After leaving the galls in late June to early July, the Eastern spruce gall adelgids become mature flying females. She lays her eggs in unprotected masses near the tips of needles. The cycle then starts again.

Apply a recommended insecticide in late September or in spring just before bud break. Dormant or summer oils will turn "blue" spruces green untill the following year when new growth emerges.

Related Resources
Home, Yard & Garden Pest Guide
Illinois Commercial Landscape and Turfgrass Pest Management Handbook
U of IL - Distance Diagnosis through Digital Imaging
U of IL - Plant Clinic