The following question was sent to the P&PDL diagnosticians here at Purdue University:
Question: I have a giant spruce growing on my lawn. About three years ago I started noticing a steady progression of entire sections of branches dying off. First the needles turn brown then fall off. The lower branches began exhibiting this first. When I put a sample of a mostly dead branch under a low powered microscope, I saw that it was teeming with appeared to be some kind of spider mite. Is there any kind of effective treatment to stop the continued defoiliation if this spruce? Is it doomed?
Answer: It sounds as if the spider mites have really taken over the plant. If these are spruce spider mites you might try a pesticide registered for spider mite control on spruce. Dormant oils will help control the mites but have been known to take the blue color out of the plant. Remember, to control mites you should consider a spray program which requires an application at 7 - 10 day intervals for 2 - 3 sprays.
-Tim Gibb, Entomologist