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Cooley Spruce Gall Diagnostic Guide

Adelges cooleyi 

Cooley spruce gall adelgid, Adelges cooleyi, commonly causes abnormal growths called galls and distortion to the new needles of Colorado spruce and Douglas fir trees. Galls appear as small pineapple shaped growths early in the season. They brown out in the summer and can be confused with seed cones. The galls rarely cause serious harm and can be covered by new growth the following season.

Trees at Risk

Colorado  spruce, Douglas fir, and many other spruce species are susceptible.







Signs of Damage

  • On spruces, pineapple-like formations (galls) are present on the tips of new growth. Galls turn brown during the summer months.
  • Galls are not formed on Douglas fir, but needles may become discolored, distorted, and prematurely drop from the tree.
Cooley Spruce Gall Signs

Whitney Cranshaw, Colorado State University,

Cooley Spruce Gall Signs

Whitney Cranshaw, Colorado State University,

Physical Appearance

  • Similar to aphids in appearance.
  • Both winged and wingless adult females are approximately 1 mm long and dark brown to black.
  • Adults on Douglas fir secrete white strands of wax that cover their bodies.
Cooley Spruce Gall Signs

Petr Kapitola, State Phytosanitary Administration,


Cooley spruce gall’s life cycle is fairly complex, as it involves multiple biological forms. Three of these biological forms take place on spruce and two on Douglas fir. The complete life cycle through all five of these forms takes at least two years to complete. The pest’s life cycle can be completed on Douglas fir alone, but the forms that take place on spruce have to find Douglas fir as the second host to complete the entire life cycle.

On Spruce:

  • Females feed in the spring and lay several hundred eggs.
  • Eggs hatch in 10-14 days.
  • Young nymphs move to new growth to feed at the base of the needles.
  • Feeding causes distorted gall formations that soon surround the young nymphs.
  • Galls dry out and brown by mid-summer.
  • Adelgids emerge from galls and move to Douglas fir or stay on the spruce.
  • Immature females overwinter at the base of terminal buds.

On Douglas fir:

  • Females that have migrated from spruce lay eggs on needles.
  • The following spring, winged females are produced and they return to the spruce to start the life cycle over again.
  • Wingless females stay on the Douglas fir and reproduce.

Treatment Strategy

Cooley spruce gall adelgid can be tough to manage. Once the galls begin to form, contact insecticides usually are ineffective because the insects are protected within galls. Galls can be pruned-out by hand in small trees. If galls are seen during the season, systemic soil application of Xytect™ should be made in late summer/fall because of the early spring activity of adults the following year. Apply Transtect™ in early spring to spruce.

  • Soil Application using Xytect 2F

    Dosage: 6 mL/inch DBH
    Timing: Late summer or fall for next year control
    Re-Treatment: Annually
    Xytect 2F Insecticide
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  • Soil Application using Transtect

    Dosage: 1 pkt treats 5 - 17 in of DBH
    Timing: Apply early spring as soil begins to thaw.
    Re-Treatment: Annually
    Transtect 70WSP Insecticide
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  • Systemic Bark Spray using Transtect

    Dosage: 6 pkts/gal water for trees <24 in DBH and 6 - 12 pkt/gal for trees >24 in DBH
    Timing: Apply early spring
    Transtect 70WSP Insecticide
    Transtect Login for pricing
  • Soil Application using Xytect 75WSP 22 packets

    Dosage: 1 pkt/24 - 48 in DBH
    Timing: Spring or fall
    Xytect 75WSP 22 packets
    Xytect 75WSP 22 packets Login for pricing
  • Foliar Spray using Up-Star Gold

    Dosage: 10.8 fl oz/100 gal water
    Timing: Apply spring before new growth or fall when insects start to overwinter
    Up-Star Gold
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A Diagnostic Guide is designed to help you identify a pest issue and management solutions. Always refer to product label for all rates and approved uses. Some images courtesy Use of the images does not imply endorsement of treatments by

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