Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES
Eastern Spruce Gall Adelgid
The
eastern spruce adelgid, is commonly referred to as an
aphid. However, aphids have long antennae and characteristic cornicles, or pipe-like tubes arising from the tip of the
abdomen. Adelgids
have short antennae and no cornicles. This pest is
found throughout all of North America, wherever its host spruces are grown. It
has also been exported to Europe.
Plants Attacked
This pest prefers Norway and white spruces, but occasionally
attacks red, black, Englemann and Colorado spruces.
Damage
The
pineapple-shaped galls greatly stunt the growth of new spruce shoots. Trees
demonstrate a wide range of susceptibility; some have many galls which kill the
branch and others having few galls which allow for continued branch growth.
Description and Life Cycle
This
relative of aphids causes small pineapple-shaped galls at the bases of
branches. The eastern spruce gall adelgid over winters as immature females (fundatrices) attached to the current year's twigs, usually
at the bases of buds. In mid-April these dark greenish-gray females continue to
grow, producing a white, waxy, cotton-like covering. Within two to three weeks,
the females mature and lay 150 to 200 olive green eggs in the wax. By this
time, the spruce buds have begun to drop their bud-sheaths and expand: The
bases of the lower needles in the bud are slightly swollen and discolored because
of the feeding by the fundatrix. The eggs hatch into
yellow nymphs (gallicolae migrans)
which move to the swollen needle bases to feed and
continue gall formation. Within a couple of weeks, the needle bases have
swollen into tightly closed 1/4-inch chambers. Unlike the Cooley spruce gall
adelgid, the eastern spruce gall adelgid only affects the lower half of a bud;
the tip grows outward in a normal manner. The gallicolae
migrans molt three times in the gall and are ready to
emerge by August and September. By this time, the gall turns brown and the
chamber walls dry, opening the escape slits. The mature nymphs crawl to needles
and molt into winged females (alate non-migrans). These winged females are feeble fliers and
usually do not leave the tree. Within two to five days, the alate
non-migrans lay up to 60 eggs under their wings and
then die. These eggs hatch into the over wintering fundatrices
which move to new buds.
Control Hints
Unlike
the Cooley spruce gall adelgid, this pest has no alternate host. The life cycle
is completed on a single suitable host plant. Well timed sprays are generally
the most effective controls.
Strategy 1: Cultural Control- Use
of Resistant Varieties - Black, red and Englemann spruces are
generally less susceptible to this pest. However, certain cultivars of Norway
and white spruces have demonstrated some resistance. Try to select uninfested
nursery stock which has not been sprayed regularly for control of this pest.
Trees lacking galls are more likely to be resistant.
Strategy 2: Chemical Control -
Dormant Oil Sprays
- Dormant oil, applied in April, is very effective against this pest. Be sure
to use good quality oil and spray before buds have doubled their winter size.
Strategy 3: Chemical Control-
Fall Insecticide Sprays - Insecticides can be applied in September and October to kill the alate non-migrans and over
wintering fundatrices.
Strategy 4: Chemical Control -
Spring Insecticide Sprays - Insecticides can be applied in mid-April before the fundatrices mature and lay eggs. This is usually before the
bud sheaths become loose.
Information obtained through the Ohio State Extension Factsheet HYG-2050-95
Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES