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Shelterbelt Centre Pest Leaflets
Cooley Spruce Gall Adelgid
Hosts: Colorado and white spruce
Appearance and Life History:
The cooley spruce gall adelgid
has a very complex life cycle
which is not fully understood.
Adelgids are a small group of
insects that are closely related
to aphids. The normal life cycle
of this adelgid consists of six
different forms of the insect
over a two-year period on two
hosts; spruce and Douglas fir.
In Saskatchewan and Manitoba
where there is no native
Douglas fir, the adelgid has the
capability of completing its life
cycle entirely on spruce. Only
the first form of adelgid causes
a formation of galls, whereas,
the remaining forms feed openly
on needles. Another form of the
cooley spruce gall adelgids
produce white, cottony
protective covers for their eggs.
These cottony covers appear as
white specks early in the spring
and continue throughout the
summer, and can cover an
entire tree during a severe
infestation.
Damage: Damage first occurs
in late May when
the new growth of the branch
tips form into cone-shaped
galls. Galls vary in length from
25 to 75 mm and 12 to 18 mm
in diameter. The galls are green
at first but later turn a
reddish-purple color. The old
galls dry out and turn a
reddish-brown color and may
remain on the branches for
several years. During a heavy
infestation, young spruce may
be severely deformed because
the buds die on the gall-infested
twigs. On established spruce,
the growth and vigor may be
reduced but trees are rarely
killed.
Control: Some control may be
achieved by picking the new
galls off as they form and
burning them. This will
improve the tree's appearance
and reduce the aphid
population. Chemical control of
the cooley spruce gall adelgid
can be achieved by applying
carbaryl or malathion in early
spring just as the buds begin to
open.
For more information contact:
PFRA Shelterbelt Centre
Indian Head, Sask. S0G 2K0
Phone: (306) 695-2284 or Fax: (306) 695-2568
E-mail: pfratree@agr.gc.ca
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