SPRUCE SPIDER MITE, (Oligonychus ununguis)
BACKGROUND
Spruce spider mites are native to North America. They are very common across their range.
They frequently reach epidemic levels and remain there for lengthy periods of time. Their
piercing/sucking feeding can do considerable damage to host trees. Spruce spider mites are not
a serious problem in natural forests, but are a significant pest of ornamental and shelterbelt trees.
DISTRIBUTION
The spruce spider mite is widely distributed throughout the temperate regions of the United
States and Canada.
DESCRIPTION OF LIFE STAGES
Mites are not insects as the adults have eight legs, rather than six. Adult spruce spider mites are
very small, being approximately 0.6 mm long. Their bodies are dark green to almost black with a
pale streak on the middle of the back. Females have a more oval abdomen than males. Eggs
are a pale yellow initially, but darken with age to reddish-brown. Eggs are spherical, 0.2 mm in
diameter and have a spike that anchors them to webbing. Larvae have six legs, are pink at first,
but turn green after feeding. Nymphs have eight legs, are 0.3 mm to 0.4 mm long and resemble
the adults. They are a mottled green colour.
Adult spruce spider mite
Spruce spider mite eggs
Image: Natural Resources Canada,
Canadian Forest Service,
Northern Forestry Centre
Image: USDA Forest Service - Region 4 Archive,
USDA Forest Service, Bugwood.org
HOST SPECIES
Spruce spider mites attack spruce, cedar, juniper, hemlock, pine, Douglas fir, Fraser fir, balsam fir
and larch. In Saskatchewan, the major hosts are native white and black spruce and the
introduced Colorado spruce.
LIFE CYCLE
Spruce spider mites have four to seven generations per year. The life cycle has five stages:
adult, egg, larva and two nymphal stages. Following mating, adult females lay eggs in autumn
under bud scales, on the undersides of twigs and at the base of needles. One female may lay up
to 50 eggs. Winter is spent in the egg stage. Larvae hatch from the eggs through May to early
June. Larvae feed and develop into nymphs. Nymphs feed and develop into adults by early
summer. Larvae, nymphs and adults all feed. The first generation feeds on old foliage, while
subsequent generations feed on the current year’s foliage. Feeding continues through the
summer and early fall. One generation may take as few as 10 to 14 days. Spider mites can
disperse on wind currents, by adults crawling from tree to tree, and by movement of nursery
stock.
SIGNS, SYMPTOMS AND DAMAGE
Spruce spider mites pierce and suck the needles causing a fine stippling that increases in
intensity until the foliage has a bleached appearance. Foliage becomes yellowish to brownish
with severe feeding and loss of needles occurs. The mites spin a fine silk webbing that can be
seen around twigs and needles. The webbing becomes more abundant as the feeding season
progresses. Repeated heavy feeding will kill seedlings and saplings. On larger trees the most
severe damage is initially on lower branches. However, over time, the entire tree becomes
infested. Larger trees can be killed following a number of years of severe feeding damage.
Spruce spider mite webbing
Stippling from spider mite feeding
Image: Thérèse Arcand, Natural Resources
Canada, Canadian Forest Service
Image: Eric R. Day, Virginia Polytechnic
Institute and State University, Bugwood.org
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Spruce spider mite severe feeding damage
Image: Eric R. Day, Virginia Polytechnic Institute and
State University, Bugwood.org.
MANAGEMENT PRESCRIPTIONS
Spruce spider mites thrive on trees when they are drought stressed. If mite populations are light,
watering trees during dry periods may help to reduce damage. Spruce spider mites can be
dislodged from trees by spraying a steady heavy flow of water from a hose. Spraying twice a
week during periods of peak feeding activity can greatly reduce the mite population and will be
less harmful to natural predators. When populations are high and damage severe, control with
commercial spray products may be necessary. Horticultural oils can be applied as a dormant
spray before new growth commences. When mites are actively feeding, insecticidal soaps or
chemical formulations such as kelthane and malathion can be used. Foliage should be sprayed
until dripping wet, normally with one treatment in late May and one in late June to early July.
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REFERENCES FOR ADDITIONAL INFORMATION
Natural Resources Canada
Canadian Forrest Service
http://www.pfc.forestry.ca/diseases/nursery/pests/mites_e.html
Spruce Spider Mite
Prairie Farm Rehabilitation Shelterbelt Centre
Agriculture and Agri-Food Canada
http://www4.agr.gc.ca/AAFC-AAC/display-afficher.do?id=1198272783112&lang=eng
Spruce Spider Mite on Fraser Fir CTN-029
North Carolina State University Christmas Tree Notes
Prepared by Jill Sidebottom, Ph.D.
Area Extension Forestry Specialist, Mountain Conifer IPM
Extension Forestry, College of Natural Resources
http://www.ces.ncsu.edu/fletcher/programs/xmas/ctnotes/ctn029.html
Spruce Spider Mite
Cornell University
Cooperative Extension of Suffolk County
http://ccesuffolk.org/assets/Horticulture-Leaflets/Spruce-Spider-Mite.pdf
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