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Aphids and Adelgids on Conifers
- Some don't even look like insects! -
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Summary: These small, sap-sucking insects are important pests in forests, landscape plants and Christmas tree plantations. Some are very difficult to control because of a waxy, protective covering that they hide under.
Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)
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What are adelgids?
 Adelgids are aphid-like insects in the genus Adelges (family Adelgidae) that feed mainly on conifers. Conifers are trees and shrubs that bear cones such as pine, spruce, hemlock, fir, and many other valuable landscape and forest species.
Visit the American Conifer Society site for general information about growing conifers.
Adelgids can be important pests in landscapes, plant nurseries, Christmas tree plantations and forests. Since both aphids and adelgids tend to be somewhat host plant-specific, adelgid identification often begins with correct identification of the host tree or shrub.
Adelgids usually cover themselves with a waxy coating (right). This wax can make mature adelgids very difficult to control with spray-type insecticides. The best control strategy is to treat the young, unwaxed, stages with an overhead spray such as insecticidal soap then treat waxed stages with a systemic insecticide like imidacloprid (Bayer Advanced Tree & Shrub Insect Control, Merit Insecticide, and others).
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hemlock woolly adelgid (Adelges tsugae) covered with white wax
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What about other aphid pests on conifers?
A number of true aphids also attack conifers but, in general, tend to be less harmful than adelgids. The conifer aphids (Cinara spp.), including the bowlegged fir aphid (lower right) occur on all conifers and feed on stems. Generally these large aphids won't harm plants unless populations are high. There are also some twig and needle-feeding aphids. The following [pdf] bulletin has information about these insects in Oregon:
Aphid and Adelgid Pests of Conifers in Oregon [pdf] This is an OSU Extension bulletin that I authored in 1994. This bulletin covers most of the important aphid and adelgid pests of conifers with details about life history, monitoring and control.
Control of aphids & adelgids on conifers
Healthy trees and shrubs can usually support a fair number of these pests without much damage. Therefore, your first efforts should be to create healthy plants through proper water, fertilizer and soil management.
If populations are high and damaging, unwaxed aphids can be effectively controlled with a strong overhead spray of plain water from the garden hose followed by treatment with insecticidal soap. You may need to repeat this several times during the summer because the soap has no residual activity.
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bowlegged fir aphid on noble fir
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Waxy, mature adelgids should be treated with a systemic insecticide like Bayer Advanced Tree & Shrub Insect Control which contains imidacloprid. This insecticide moves around in the plant's vascular system and poisons aphids or adelgids when they feed.
Related information:
Conifer root aphid Prociphilus americanus in Oregon (1998) [pdf] This is an unpublished summary used in a 1998 short course. Note: control suggestions may be outdated in this 1998 paper.
Balsam Woolly Adelgid & Balsam Twig Aphid [pdf] This is an unpublished handout used in a 1998 short course. Basic life history information. Note: control suggestions may be outdated in this 1998 paper.
The Pest Management Store
Identification guides, reference and gardening books, etc.
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Identify Aphids and Adelgids on Some Conifers
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This table will help you identify some of the aphids and adelgids on Douglas-fir, true firs and spruce. Because these insects are somewhat host plant specific it is sometimes possible to base identification on the host plant itself. The table lists only a few of the aphid and adelgids that can be found on these conifers.
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Douglas-fir (Pseudotsuga menziesii)
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Large, dark colored aphids without waxy covering. Produce large amounts of honeydew which may attract yellowjackets and ants. ===>
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conifer aphids (Cinara sp.)
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Small, dark "crawlers" on needles in late spring and/or white cottony tufts of wax on needles before bud break or after mid-June. ===>
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Cooley spruce gall adelgid (Adelges cooleyi)
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True firs (Abies sp.)
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Large, dark colored aphids without waxy covering. Produce large amounts of honeydew which may attract yellowjackets and ants. ===>
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conifer aphids (Cinara sp.)
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Swelling of branch nodes caused by very small, waxy adelgids. Trunk and branches covered with patches of white, waxy material. ===>
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balsam woolly adelgid (Adelges piceae)
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Twisting of new needle growth. Small greenish yellow or larger bluish gray (stem mother) aphids. Wax and honeydew produced by aphids may mat needles together and attract yellowjackets. ===>
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balsam twig aphid (Mindarus abietinus)
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Spruce (Picea sp.)
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Large, dark colored aphids without waxy covering. Produce large amounts of honeydew which may attract yellowjackets and ants. ===>
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conifer aphids (Cinara sp.)
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Pineapple-shape galls or cones on branch tips. ===>
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Cooley spruce gall adelgid (Adelges cooleyi)
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Twisting of new needle growth. Small greenish yellow or larger bluish gray (stem mother) aphids. Wax and honeydew produced by aphids may mat needles together and attract yellowjackets. ===>
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balsam twig aphid (Mindarus abietinus)
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Older needles shed, especially on lower, shaded portions of tree. Aphids peak in late winter, disappear by summer. Small, green aphids. ===>
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spruce aphid (Elatobium abietinum)
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