Needle cast, caused by the fungus Rhizosphaera kalkhoffii , can be a serious disease of blue spruce in nursery and Christmas tree production, and occasionally in landscape settings. The disease attacks needles in the lower portion of the tree crown first, then gradually moves upward, killing the needles on progressively higher branches. Symptoms first appear in late summer or fall when mature needles on the lower portion of the crown begin to turn yellow. The diseased needles remain attached to the tree throughout the winter. The following spring, needles begin to turn purple and drop from the branch.
Most defoliation occurs late in the summer the second year after infection.
Because stomata are linearly arranged, the black dots, or fruiting structures of the fungus, characteristically line up in neat rows on the needles. Affected branches are eventually defoliated and killed by the fungus. Disease development is favored by poor air circulation and high relative humidities. Control of unwanted weeds and shrubs in the vicinity of trees is important in increasing air movement and decreasing environmental conditions necessary for infection. Fungicide applications may be required to suppress further infection on diseased trees.