NC State Extension Publications

Description and Biology

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The most common spider mite pest of conifers in North Carolina is the spruce spider mite, Oligonychus ununguis. The spruce spider mite is one of the "cool weather" mites. Spruce spider mite eggs are spherical, but slightly flattened and have a diagnostic stipe (thread) projecting up from the center. The first stage (the larva) is only slightly larger than the egg. Larvae have six legs. Later immature stages are called nymphs. Like adults, nymphs have eight legs. Spruce spider mites are relatively inactive in cold weather and tend to die out in hot weather. Only the eggs survive hot summers and very cold winters. At upper elevations, the spruce spider mite may be active all summer long. Males mate with females as soon as the females molt into the adult stage and females soon begin laying eggs. Most reproduction takes place in spring and fall. Spruce spider mites also overwinter as eggs usually laid at the base of needles. In April and May the eggs hatch and larval mites begin feeding and developing. Most feeding damage takes place in spring and fall. These mites usually do not cause dieback, which is usually caused by the minute cypress scale insect or some other problem.

Spruce spider mite damage on juniper.

Spruce spider mite damage on juniper.

Spruce spider mites on juniper.

Spruce spider mites on juniper.

Spruce spider mite eggs have a slender stipe.

Spruce spider mite eggs have a slender stipe.

Male spruce spider mite waiting for female to molt.

Male spruce spider mite waiting for female to molt.

Host Plants

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Spruce spider mites feed on spruce, arborvitae, Douglas fir, Fraser fir, hemlock, juniper, pine, and other conifers in nurseries and landscapes. Spruce spider mites feed by poking their sharp, scissor-like mouthparts into a needle, injecting saliva, and then sucking out the predigested "soup." They do most of their damage in spring and fall. However, the foliage may not turn yellowish-brown until June or July after the mites have already died out for the summer (only the eggs survive the summer in the Piedmont and Coastal Plain).

Residential Recommendation

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Because the spruce spider mite tends to feed on older growth, thorough coverage is necessary to get the pesticide inside the plant where the mites are feeding. This mite is not particularly resistant to miticides. Consider using one of the horticultural oils because oils are not only effective for spider mites, they also control other pests of conifers such as aphids, juniper scale, and minute cypress scale.

References

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For assistance with a specific problem, contact your local Cooperative Extension Center.

This Factsheet has not been peer reviewed.

Author

Professor Emeritus
Entomology and Plant Pathology

Publication date: April 19, 2013
Revised: Oct. 15, 2019

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