The Q&A Archives: Spruce Tree Disorders

Question: My blue spruce tree, 30 ft tall), has it's needles turning purple, then brown and falling off. Has been treated for possible needle cast (wasn't),beetles(wasn't), and now am told maybe it is lacking phosporus......I have already had one die this year from it, the other two are looking the same....Help! The county extension office feels it is probably the phosporus. So I put some high level (45%) phosporus on it today. But, need help. Thanks in advance.

Answer: The symptoms you describe sound like Rhizosphaera Needle Cast. It's a common disease on both Colorado Blue Spruce and Engelmann Spruce. If you've treated the tree with a fungicide, then you may only have to wait for the disease to be controlled by the fungicide. Needle cast usually attacks current season needles, which turn purplish brown. The brown needles are then shed the following spring and summer. Your extension office should be able to detect tiny fruiting spores on the affected needles by inspecting them under a microscope. If older growth is affected as well, then I'd consider a root problem with the tree. Lack of phosphorus could cause purplish needles, but root rot is a more likely cause. Spruces weakened by adverse growing conditions such as drought, winter injury, insects or mechanical injuries are more susceptible to disease problems. Perhaps your trees have been struggling for years and are only now showing symptoms. It's been my experience that extension offices do their level best to diagnose plant problems, but you always have the option of asking that the specimen be sent directly to the university for a second opinion. If you make this request, be prepared to fill out a multi-page form on the history of your tree and exactly what control methods you've used. I think time is of the essence to save your trees. Contact your extension office again and ask that the specimen be sent to University of Idaho, Ag Science Bldg., Moscow, ID 83844-2338. Good luck with your trees!

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