On Colorado blue and Norway spruce trees, green or purplish shaped growths
(galls) up to 2 inches long appear on the tip of branches
of trees. The
galls turn brown as the summer progresses and are very noticeable by fall.
The galls are generally not life threatening to the trees, however, in
large numbers, they can become quite unsightly.
On Douglas fir trees, white, cottony tufts appear on the undersides
of needles in midsummer. Small, (1/8 inch) blackish insects may be found
under the tufts. Needles are spotted yellow and may be distorted.
These growths are caused by an insect called the Cooley spruce
gall aphid. In the late spring, it feeds, matures and then lays eggs at
the base of needles near the tip of the branch of spruce trees. When the
eggs hatch, the young insects move to growing needles and begin to suck
the juices from them. This damage stimulates the plant to form the galls.
aphids live and feed inside the chambers of the gall until about
July when the mature insects emerge. They develop wings and fly to a Douglas
fir or another spruce tree. On the Douglas fir, the aphids lay eggs and
produce a generation of woolly aphids. Some of these aphids develop wings
and fly back to the spruce to start the cycle all over again the next spring.
On small spruce trees or where practical, cut off the galls as
they are developing in the early summer.
To prevent establishment of the galls on spruce, spray with
an insecticide labeled for this problem in the spring as the new buds at the tip of the branch are elongating.
On Douglas fir, spray with
an insecticide labeled for Cooley spruce gall when the new
growth is expanding to control hatching insects.
Commercial spray companies may soil inject a product called Merit in
the fall for control of spruce gall aphids (adelgids).