October 2014 Plant Disease Update
Rhizosphaera needle cast, caused by the fungus Rhizosphaera kalkhoffii, is a common problem in landscape and Christmas tree plantings of blue spruce, but it is also a problem on other spruce, such as Norway spruce. Although symptoms appear in the fall, the fungus that causes the disease infects needles in the spring.
Rhizosphaera needle cast is best managed with spring applications of protectant fungicides; applications in the fall will not be effective. Sprays should begin when new growth is 1/2" to 2" long and be repeated at 2 to 4-week intervals or at shorter intervals during heavy rainfall. New infections can occur throughout the summer, but sprays are most effective during the early part of the summer when conditions are typically wetter.
When trees have suffered significant defoliation it can take several years of fungicide treatment before the tree regains full foliage. Stigmina needle cast is another fungal needle cast disease of spruce with similar symptoms and control recommendations to Rhizosphaera. Spruce mite infestation can also cause spruce needles to brown and drop, and, like Rhizosphaera needle cast, the problem starts at the bottom of the tree and appears to move upward.