Answer: I'm afraid all spruces and arborvitaes are susceptible to spider mite infestations. You can discourage the pests if you periodically hose your shrubs down. Spider mites like dry conditions and washing them off will convince them to find another home. Be sure to direct the spray towards the inner branches. The damage can be pruned away or you can just allow it to die back and be replaced naturally by the spruce.
I would not recommend chemical controls. Various insects and predatory mites feed on spider mites and provide a high level of natural control. One group of small, dark-colored lady beetles known as the "spider mite destroyers" (Stethorus species) are specialized predators of spider mites. Minute pirate bugs, big-eyed bugs (Geocoris species) and predatory thrips can be important natural enemies.
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