of Rhode Island GreenShare Factsheets
Two species of adelgids, often incorrectly called aphids,
can damage at least three species of spruce and will also attack
Douglas Fir. These insects are not usually serious pests, especially
in forest conditions, but damage can be quite disfiguring when
trees are planted in monoculture situations such as Christmas
Both the Eastern spruce gall adelgid (Adelgis abietis) and
the Cooley spruce gall adelgid (Adelgis cooleyi) are
widely distributed throughout the Northeast. Eastern spruce
gall feeding damage typically causes galls 12 to 25 mm (1/2-1
inch) long to form in the crotches of young twigs on both Norway
and white spruces. Feeding by the Cooley spruce gall adelgid
will cause large, 2 1/2 - 8 cm (1-3 inch), galls to form on
the tips of Colorado blue spruce. Cooley spruce gall feeding
injury on Douglas fir causes yellow spots on the needles. If
uncontrolled, the needles will bend and the tree will be covered
with adults that look like tiny cotton balls.
The Eastern spruce gall adelgid overwinters as an immature
female under a thread-like cover of wax near the base of the
buds. In the spring, when buds begin to swell, the adelgids
become active and can lay up to 200 eggs at the base of the
bud. Young nymphs hatch in less than two weeks and immediately
begin feeding on the needles of emerging shoots. Continued
feeding induces an abnormal growth, or pineapple-shaped gall,
to form at the base of the branch. Each gall has cells, or
locules, which house an individual growing nymph. In late summer
or early fall, the galls dry and open, releasing the mature
adelgids which then lay eggs on the needle tips. The overwintering
adults hatch from these eggs.
The Cooley spruce gall adelgid overwinters
as an immature female beneath bark scales on spruce or Douglas
fir. In the
spring they lay their eggs under a cottony, waxy covering which
can be quite conspicuous. When the eggs hatch in the spring,
the nymphs crawl to the developing buds and begin to feed.
This feeding results in swelling of tissue, and eventually
a gall will develop on the tips of Colorado blue spruce branches.
The young adelgids will live in their individual cells within
the gall until mid-summer, when winged adults emerge and migrate
to other spruce or Douglas Fir.
Many references incorrectly
state that the Cooley spruce gall adelgid requires both Colorado
blue spruce and Douglas Fir to complete its lifecycle--in
fact, in the absence of the alternate host Douglas Fir, the
gall adelgid can complete its lifecycle on spruce.
Eastern spruce gall adelgid:
- Do not fertilize heavily infested trees. There is some
evidence that fertilizing without chemical control will actually
enhance insect population growth.
- If practical, hand pick and burn or destroy galls before
insects emerge (green stage) It is too late after the galls
turn brown and the holes appear. Also, if practical, rogue
out most heavily infested plants early on to encourage growth
of the more resistant trees.
- Horticultural oil applied when plants are dormant (mid-April
to early May) is reasonably effective. Another application
of horticultural oil or insecticidal soap in mid- to late September,
as insects emerges from galls, will provide excellent control.
Cooley spruce gall adelgid:
Spruce - Do not fertilize heavily-infested trees.
- If practical, hand pick and destroy galls at the
- Rogue most susceptible plants when young.
- Do not plant Colorado blue spruce close to Douglas fir.
- Apply horticultural oil at bud-break. Make second application in late-July
Douglas Fir - No effective parasites or predators have
been found; chemical control remains the best option. Apply
horticultural oil when trees are dormant, but use caution on
trees that will be sold in the same year, as oils can reduce
tree color. Apply in early May and, if necessary, again in
By David Wallace, Plant
Protection Specialist, 1999
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
of Rhode Island Cooperative Extension provides equal program