Spruce needle cast disease is caused by the fungus Rhizosphaera kalkhoffii. The disease causes significant defoliation of spruces, especially Colorado blue spruce, in landscapes and Christmas tree plantations. The fungus also infects Douglas fir, and Austrian, mugo, and white pines. Rhizosphaera needle cast is characterized by rows of tiny, fuzzy, black fungal fruiting bodies emerging from the surface of infected green and yellowing needles. Diseased needles turn brown or purplish-brown a few months to a year after infection and may drop from the tree.
To reduce needle cast disease, spruce trees need to be planted where they get sun and good air movement. Pruning out diseased branches may help provide ventilation. Fungicide use may be justified in Christmas tree plantings. Trees can be sprayed with fungicide when the new needles are half developed and again when they are full length. Fungicide treatments are intended to prevent new infections, but two years of treatment may restore moderately affected trees to full foliage. Severely affected trees may require more years of treatment.
Contact your local Extension office for fungicide recommendations.
