Iowa State University Extension - Wapello County Spruce mite injury is similar to that caused by other common spider mites. Winter is passed in the egg stage at the base of needles. The mites suck sap from leaves of diciduous trees and shrubs and from needles of evergreens, leaving them yellowed, gray, or dusty-looking.
Greatest damage is done during periods of dry weather.
There are many generations each summer. Iowa State University Extension, Ames, Iowa.