Problem: Rhizosphaera Needle Cast
This disease is caused by a fungus (Rhizosphaera kalkhoffii) infecting only spruce trees. It is most common on Colorado blue spruce (Picea pungens) but also infects white spruce (P. glauca) and occasionally Norway spruce (P. abies). From late spring to fall, rain splashes spores from diseased needles-on the tree and the ground-onto young healthy needles or to stressed older needles. The fungus grows within the needles for almost a year with no symptoms; then needles turn yellow or purple-brown and die. The cycle begins anew the next spring, Spores infect leaves that are wet for at least 48 hours, so they are worse during wet springs. The fungus does not usually kill trees, but dead branches spoil the appearance.
Apply a fungicide labeled for this disease, following label directions. Watch for reinfection. Clean up and dispose of fallen needles before spring growth begins. Water in summer and fertilize in the spring to keep trees growing vigorously and prevent needle cast. Avoid wetting needles watering the lawn.