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Adelgids
- 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, Douglas-fir, true fir, and
many other valuable landscape and forest species.
Like aphids, adelgids feed by tapping into their
host plants and withdrawing plant sap. Infestations
can cause branch dieback, growth deformation and in
severe outbreaks even death of the host plant.
Entire forests can be killed by certain adelgids
such as the hemlock woolly adelgid (see photo
right).
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 usually
begins with correct identification of the host tree
or shrub (see below).
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 (see Merit
Insecticide).
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hemlock
woolly adelgid (Adelges tsugae);
the adelgids are covered with white wax
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Tree identification
If you know what
kind of tree you have use the table below to
identify the respective adelgid and aphids pests. If
you are unsure of your plant's identification use
this tree
identification key from Oregon State University.
Use the "dichotomous key" link to identify an
unknown. Once you know the plant, use the table
below to identify the aphids and adelgids that can
infest your type of plant.
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Control of aphids &
adelgids
Healthy trees and shrubs
can usually tolerate 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 (see Using
Insecticidal Soap to Control Aphids). You may
need to repeat this several times during the summer
because the soap has no residual activity.
Waxy, mature adelgids
should be treated with a systemic insecticide like
imidacloprid (see above). This insecticide moves
around in the plant's vascular system and poisons
aphids or adelgids when they feed
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How to identify aphids
and adelgids on some conifers
The table below can 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 some of the more
common aphid and adelgids that can be found on these
trees.
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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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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.
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.
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Mission: To
provide accurate, up-to-date and unbiased information
for solving common insect and mite problems around
your home, business and landscape using least-toxic
methods.
Jack DeAngelis,
Ph.D.
Please see the Disclaimer statements as
well.
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