What is causing my spruce trees to develop brown needles?
I have approximately 35 Black Hills spruce and blue spruce. A large percentage are developing brown needles scattered throughout the trees, some more so than others. Someone mentioned that it may be caused by ?? rhizo?? needle cast. Can you recommend a treatment or fertilizer treatment that may help? All of the trees are approximately 21 years old.
There are several needle fungi that can cause brown needles. It is often one of two different types—Cytospora Canker and Rhizosphaera Needle Cast. Trees with Rhizosphaera needle cast are usually affected first on the inside of the tree, working out, and at the bottom of the tree, working up. This disease is most apparent on older needles on the tree. If you see scattered branches with areas on the bark leaking abundant white, sticky resin on dead branches then they have Cytospora canker. It could also be mite damage. Mites are tiny spider-like creatures that suck the sap from spruce needles, so that when viewed under magnification the needles appear speckled with yellow flecks. You can scout for mites by shaking a symptomatic branch over a white sheet of paper and then looking for tiny, moving dots (mites). The following site has more information. http://www.extension.umn.edu/distribution/horticulture/M1265.html
I hope this is helpful. Thanks for contacting AaE.