One of the most common spider mites occurring in nursery production is the spruce spider mite (SSM), Oligonychus ununguis. It is the predominant spider mite affecting conifers in the Pacific northwest and elsewhere.
SSM overwinters in the egg stage (versus as a gravid female as with two-spotted mites). They are usually found at the base of the needles or scales and are reddish in color. Eggs hatch (eclose) in the spring when Bradford callery pears and Manchu cherry are in full bloom or around 162 degree days (Base 50F).
Biological Control of spruce spider mites for growers in the PNW can be achieved with the predatory mite, Neosieulus fallacis. See the link on biological control of two-spotted spider mites for more information.
Dormant oils can be use to smother the eggs in the fall or early spring. It is not recommended to use oil on glaucus-colored (or blue) conifers as the color may be reduced. Many growers target the egg hatch to apply ovicide/larvicides for long-lasting effect. These mites prefer cool temperatures and can build up rapidly at optimal temperatures (60-70 F). Damage often shows up in summer after heavy spring feeding.
The following links have useful images and information about spruce spider mite.
Spruce spider mite: Pennsylvania State University. This informative website has information available on spruce spider mite in Christmas trees.
Shetlar, Dave. Spruce spider mite. The Ohio State University.
Spruce spider mite fact sheet. PNW Insect Management Handbook (online). Good information for Pacific Northwest SSM populations.
Last revision: 18 April 2014
Author: R.L. Rosetta, Extension Nursery Integrated Pest Management, Department of Horticulture, Oregon State University/NWREC.
Spruce spider mite damage on arbovitae (note the discolored tree in the middle of the picture)
Spruce spider mite damage on arbovitae
Spruce spider mite damage and eggs