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Shelterbelt Centre Pest Leaflets
Spruce Spider Mite
Hosts: Colorado and white
spruce.
Appearance and Life History:
The spruce spider mite
completes up to 8 generations a
year. Adult mites are
microscopic (0.5 mm) and dark
green to dark brown in color.
Feeding begins in mid-May and
continues throughout the
growing season.
Over-wintering eggs are
produced from September until
a severe frost.
Damage: The spruce spider
mite injures the needles by
inserting its slender mouthparts
and sucking out the sap. The
puncture causes a stippled,
bleached discoloration. In
severe infestations the needles
become dingy yellow or
brownish and often needles dry
and drop off. Damage is usually
first noticed on the lower inside
branches but spreads upward
and outward as the infestation
progresses. The mites spin fine
silken webbing throughout the
twigs and needles. The
webbing is most noticeable on
the underside of the branches
where dust particles, dead
needles and dead mites adhere.
In spruce plantings, infestations
can persist for years resulting in
reduced
tree vigor and eventually death.
Recently planted trees, nursery
seedlings, or trees under stress
are especially susceptible to
serious injury. To check for
mite infestations, vigorously
shake a branch over a piece of
white paper, then rub your hand
across the paper or press the
paper in half. If red smears
appear, mites are probably
present. Trees should be
checked regularly since mite
populations can increase
rapidly.
Control: Heavy rain
accompanied by high winds and
extreme temperatures are means
of natural control. Some control
can be achieved by washing
infested trees with a strong jet
of water. For shelterbelts or
large trees, the following
insecticides can be used:
diazinon, dicofol, or malathion.
Insecticides must be applied at
high pressure so the spray
penetrates the inner branches
and webbing. A second
application may be required
two weeks after the initial
spray.
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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