Insect
and Disease Fact Sheet Compliments of New Century
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Cooley Spruce Gall Adelgid
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The
Cooley spruce gall adelgid, Adelges
cooleyi (Gillette), is often called an aphid
but it is actually a closely related group of insects. Adelgids
have short antennae and no cornicles (pipe-like
organs on the tip of the abdomen of aphids). This pest is found wherever its
hosts are grown. It can be found across North America and it is now found
worldwide where its hosts have been imported. Plants Attacked Colorado
spruce and Douglas-fir are the two major hosts but this adelgid
occasionally causes galls on Englemann and Sitka
spruces. |
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Damage On
spruces, this pest forms pine cone shaped galls from the newly expanding
buds. These galls eventually die, resulting in slowed growth of the spruce
tree and sparsely filled in branches. Many people think that the galls are
seed cones and a few galls may not warrant control. Heavily infested trees
produce unsuitable growth and need periodic protection. Description and Life Cycle The
Cooley spruce gall adelgid has four distinct forms
which can be found on Colorado spruce. In nature, this pest also flies to Douglas
fir, its alternate host, where it lives on the needles. On Colorado spruce,
the most important form of this insect is the one responsible for forming the
spiny galls from the expanding buds. |
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On
spruce, the adelgid overwinters
as an immature female (the fundatrix) attached to
branches at the base of new buds. In March and April, before the buds break,
these fundatrices suck out the newly flowing sap and
.mature. As they mature, they secrete long waxy filaments over the body in which
are laid 150 to 200 eggs. By this time the spruce buds have swollen and the bud
sheaths have begun to loosen. Within seven to 10 days, the eggs hatch into
yellow nymphs, called gallicolae migrans,
which crawl to the bases of the needles of the new bud. These needle bases have
already begun to swell from the fundatrices' feeding.
Usually these affected bud bases are distinctly pink or yellow in color. The gallicolae begin to suck sap from the needle bases and
produce a substance which causes the needle bases to continue to expand.
Eventually the needle bases swell into interlocking chambers which protect the
developing nymphs. The gallicolae shed their skin
three times within the gall. By late July to early August, the galls turn brown
and the walls of the chambers dry, leaving openings for the adelgids
to escape. The mature nymphs crawl to nearby spruce needles and molt into dark
brown, winged adults which can fly to Douglas- fir. There is good evidence that
some of these winged forms can also produce another generation on the spruce
without traveling to the Douglas-fir. In the fall, usually September, winged
forms of the adelgid (sexuparae)
return to the spruce from the Douglas-fir to lay eggs for the sexual generation
(sexuales). The sexuales
are wingless males and females which feed at the needle bases and then move to
the center of the tree to mate, lay eggs and die. By
October and early November, these eggs hatch into the over wintering fundatrices which move to the bases of next year's buds.
Control Hints
In the
past, people were encouraged to avoid growing Colorado spruce next to
Douglas-fir because of the adelgids' life cycle. We
now know that the adelgid can complete its life cycle
on either host and winged forms can migrate several miles in search of their
alternate host. A well timed spray schedule is the best control technique or
attempt to find trees which demonstrate resistance.
Strategy 1: Cultural Control- Use
Resistant Plants
- Some Colorado spruce varieties and provenances are apparently less prone to
attack by this adelgid. More work is needed to
identify good resistant stock. Trees in plantations which have not been
regularly sprayed and do not have galls are probably resistant. These should be
selected for landscape use.
Strategy 2: Cultural/Mechanical
Control - Pruning Galls - Galls which are still green, usually before mid-July, can be
picked off the trees and destroyed. This kills the adelgids
still trapped within the gall. This technique is only useful where the trees
have a few galls. This technique will not prohibit the formation of galls in
the next season.
Strategy 3: Chemical Control -
Dormant Oil Sprays
- Dormant oil sprays have been used to control this pest. Fall sprays are
applied in late October and early November while spring sprays are applied
before bud swell. Great care must be taken so as not to spray actively growing
trees as this will result possible burn of the new growth.
Strategy 4: Chemical Control - Fall Insecticide Sprays - Insecticides can be applied with good
success. Apply sprays so as to thoroughly cover branches and buds.
Strategy 5: Chemical Control -
Spring Insecticide Sprays - Insecticides should be applied in early spring, mid-April, before
the fundatrices lay eggs. In order to time these
sprays, look at the bases of spruce buds and as soon as the waxy filaments
begin to appear, sprays should be applied. If eggs have been laid, an
application of a long residual insecticide may catch the migrating nymphs.
Information obtained through the Ohio State Extension Factsheet HYG-2052-95
Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES