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Shelterbelt Centre Pest Leaflets
Spruce Budworm
Hosts: Colorado spruce, white
spruce, balsam fir and other
spruces.
Appearance and Life History:
In July to early August, spruce
budworm moths deposit about
100 eggs each, in clusters of 15
to 50 on the underside of
needles. Within two weeks,
larvae emerge and begin to
construct overwintering shelters
of silk. The larvae do not feed
prior to overwintering. Shortly
before the buds begin to expand
in the spring, the small larvae
begin feeding on old needles.
As the buds break the larvae
move to the new succulent
needles and feed for 3 to 5
weeks. Full grown larvae are
20 to 25 mm in length and have
a shiny dark-brown head and a
reddish-brown body with
whitish or yellowish spots.
Pupation occurs within the
trees, with adults emerging in
about 10 days. The budworm
has one generation per year.
Damage: Initially the larvae
mine the previous year's
needles and cause minimal
damage. When the larvae move
to the new needles, they form
protective shelters by tying the
needles and developing shoots together with
webbing. Each larva may
construct several shelters
during their development.
Damage is often most
noticeable in the crowns of the
trees where the foliage appears
reddish-brown and scorched.
The larvae are wasteful feeders
and leave dried, partially
consumed needles on the trees.
During severe infestations, the
budworm can completely
defoliate all new foliage along
with some old needles.
Repeated severe infestations
can kill the tops of the trees in 3
years and whole trees in 5
years.
Control: Spruce budworm
populations are generally
regulated by natural factors and
require control only during
epidemic outbreaks. Where
practical, hand pick the larvae
from the tree early in the
season. Insecticides registered
for budworm control include:
Bacillus thuringiensis,
dimethoate, malathion and
trichlorfon. These products are
also registered for aerial
application.
For more information contact:
PFRA Shelterbelt Centre
Indian Head, Sask. S0G 2K0
Phone: (306) 695-2284 or Fax: (306) 695-2568
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