One of the most common diseases of ornamental spruce trees is Rhizosphaera needle cast, caused by the fungus Rhizosphaera kalkhoffii . Colorado blue spruce (Picea pungens) is highly susceptible and can sustain severe damage. White spruce (P. glauca) and its variant Black Hills spruce are intermediate in resistance, while Norway spruce (P. abies) is relatively resistant. Sometimes young trees are killed by the pathogen, but more commonly branches lose their needles resulting in misshapen trees.
The spores of Rhizosphaera are spread most easily by rain splashes. Pruning the tree to increase air circulation will help reduce infections. There are also fungicides that may be applied systemically.