Rhizosphaera kalkhoffii is a fungus that affects Colorado blue spruce causing needle cast.  The first sign of Rhizosphaera on the tree is the loss of the innermost needles on the lower branches of the tree.  The fungus will continue to defoliate the tree from the ground up killing lower branches and making the tree unsightly unless steps are taken to protect the tree.  One of the best ways to protect blue spruce is to keep the plant as healthy as possible and water during periods of prolonged drought.  studies show that if a tree is under stress it is more likely to be affected by Rhizosphaera.  Fungicides can be used to control Rhizosphaera.