We occasionally receive spruce samples in the Plant Disease Clinic that show yellowing of the needles, sometimes only older needles and sometimes both older and younger needles. Such symptoms are rarely a result of infectious disease.
Yellowing of spruce may be caused by a variety of noninfectious stresses, particularly problems with the roots. Such stresses include problems with the site, such as too wet or too dry a site, or excessively compacted soil. Problems with planting are also a common culprit. Such problems can include being planted too deep, which can lead to development of coiled girdling roots around the trunk, or being planted with synthetic burlap or wire intact over the roots or stem, restricting free growth. Injuries to the trunk or roots can also cause these symptoms. Unfortunately, there is little that can be done to alleviate problems from poor planting or a poor site. Applying fungicides, insecticides, or fertilizer is unlikely to help the situation. These problems emphasize the importance of starting with an appropriate site for a tree, and planting the tree properly.
An overall yellow appearance on spruce may also be caused by spider mites. Such damage typically appears as yellow speckles on the needles when viewed under magnification. For more information on spider mites on conifers, see this article.