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On
Norway spruce trees and occasionally white, black and
red spruce, small, greenish growths appear where small
side branches meet the stem. The galls turn brown as the
summer progresses and are more noticeable by fall. The
galls are generally not life threatening to the trees,
however, in large numbers, they can become quite
unsightly.
Growth will continue past the galls but the branch may become stunted.
When large numbers of galls are present, the stems may become weaker and
more prone to dropping off in wind storms.
Problem:
These growths are caused by an insect called the Eastern spruce
gall aphid. The insect spends the winter at the base of a terminal bud.
When buds begin to grow in the spring, the
aphids lay clusters of several
hundred eggs that are covered with white, waxy threads. The young that
hatch from these eggs feed on developing needles. They suck the juices
from the needles, inducing the formation of galls that then enclose them.
The aphids live and feed in chambers inside the galls. In mid to late summer,
the galls turn brown and crack open. Aphids that emerge lay eggs near the
tip of the needles. The young that hatch from these eggs spend the winter
at the base of the buds.
A similar problem on Colorado blue spruce trees is caused by the Cooley
spruce gall. These growths, however, are formed at the tips of the branches.
The Eastern spruce galls form near where a twig joins a stem.
Control Measures
To
prevent the formation of galls, trees would have to be
sprayed with an insecticide labeled for Eastern spruce
gall just before the
new growth begins to open. Timing is critical since once the galls begin
to form and the insects are inside the gall, sprays will be ineffective.
A second spray in the fall after the galls have turned brown and have cracked
open will also help control the problem. |
