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Spruce Spider Mite Fact Sheet
Fact Sheets
> Insect Fact Sheets > Spruce
Spider Mite
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| Spruce spide rmite adult
-- Photo courtesy of Michael Masiuk |
The spruce spider mite, Oligonychus ununguis (Jacobi) is a
common pest of landscape conifers in Pennsylvania. This tiny
eight-legged animal does best in the cool spring and fall weather
with severe infestations causing discolored foliage, unthrifty
looking plants and premature leaf drop. While feeding occurs
in the fall and spring, often the damage does not become apparent
until the heat of the summer.
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Spruce spider mite damage
on
c anadian hemlock -- Photo courtesy of Michael Masiuk |
Plants Attacked
In Pennsylvania, spruce spider mites have been found on 43
different conifer species but are most commonly found on the
following plants: Abies (fir), Juniperus (juniper), Thuja (arborvitae),
Tsuga (hemlock), Picea (Spruce) and Psuedotsuga (Douglas-fir).
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Insect Identification
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Red colored overwintering
eggs of the Spruce spider mite eggs found at the base of
a hemlock needle
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Spruce spider mite adult
-- Photo courtesy of PA Dept. of Agriculture |
This oval-shaped mite is small (about
1/50”), and with all eight legs stretched out would just
cover the period at the end of this sentence. Considerable color
variation exists depending upon its age, time of the year
and host plant. Newly hatched larvae are pinkish in color, but
turn dark green or dark red after initial feeding. The overwintering
red eggs are found on the bark of small branches on the host
plant. Many spider mites produce webbing, particularly when
they occur in high populations, providing protection from natural
enemies and heavy rainfalls. |
Life History
| Winter |
Red eggs found on the bark of small branches. |
| Spring |
Egg hatch occurs as early as mid-March, but most eggs hatch
by mid-April. Young mites feed on the previous years foliage and
do not attack the current season’s growth until it hardens
off in summer. Spider mites thrive when daytime temperatures
are in the 60’s and 70’s. |
| Summer |
When the daily temperatures consistently exceed the the mid
80’s, adults become inactive and populations decline due
to an increase in predatory mites and insects. If temperatures
remain over 90 F for an extended period, the adults become dormant
and lay tan or salmon colored eggs that only hatch when cooler
temperatures return in late summer/early fall. |
| Fall |
Adult mite feeding activity resumes and continues until late
fall. Adult females lay eggs on the bark of small branches, starting
in early September and continuing until a hard frost occurs. |
Damage Symptoms
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| Spruce
spider mite feeding damage Eastern Arborvitae
-- Photo courtesy of Michael Masiuk |
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Spruce
spider mite damage
Alberta Spruce -- Photo
courtesy of Eric Vorodi |
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| Webbing
from spruce spider mite
-- Photo courtesy of David Shetlar |
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Adults feed by inserting their mouthparts
into the foliage and withdrawing plant fluids, which results in a
speckled appearance to the foliage. This ‘stippling’ increases in
intensity until the foliage can appear bronze or bleached depending
upon the host plant. Severe infestations result in needle drop.
Webbing of fine silk surrounding the needles and twigs often accompanies
high populations, protecting the mites from natural enemies.
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Monitoring
| Scouting for spruce spider mite eggs can be done in late summer and early spring, just prior to the onset of the 60-70 degree temperatures that favor feeding activity. A hand lens with 10 to 15 power magnification is required to see the eggs. Adult mite activity can be assessed by holding a white piece of paper under a branch and striking the branch three or four times to dislodge the mites. Spruce spider mites will appear as tiny black or gray-green spots moving slowly on the paper. |
Management Options
| Biological |
There are several naturally occurring predators
of spruce spider mites in the landscape. Predatory mites, lady
beetles, minute pirate bugs, and dusty wings can keep the spruce
spider populations in check during the summer months but there
is often a lag time between the build-up of spider mite populations
and predators due to slower reproductive rates. Control of spider
mites through the purchase and release of predators in the landscape
is currently being researched. |
| Mechanical |
Spider mites can be dislodged from plants
during heavy rains. Spraying the plant with a steady forceful
jet of water from a hose twice a week during periods of peak mite
activity can greatly reduce the mite population and help conserve
the natural predators. |
| Cultural |
Spider mites thrive on plants under drought stress
, therefore, provide adequate water during dry periods. |
| Chemical |
Most spider mites can be managed with the use of insecticidal
soap or horticultural oils. Both of these products can remove
the silvery blue-gray color from the needles of Picea pungens
var. glauca and its many cultivars.
Control
measures for spruce spider mites. |
 download
Spruce Spider Mite Fact Sheet
Authored by: Michael Masiuk, Commercial Horticulture
Extension Agent, Allegheny County, Pennsylvania
Last Updated: Tuesday, February 11, 2003
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