Recognizing Deciduous Tree and Rhizosparea Needle Cast of Spruce
Rhizosphaera needle cast can be a serious disease of blue spruce. The presence of this disease in landscape plantings illustrates the importance of properly spacing plant material. Proper spacing often means increased resistance to certain diseases because it allows for increased air movement and, thus, decreases the environmental conditions necessary for some fungal infections.
The Rhizosphaera fungus first attacks needles in the lower portion of the tree, but it progresses to successively higher branches until the entire tree is involved. The symptoms appear in late summer or fall when mature needles on the lower portion of the tree begin to turn yellow. Diseased needles remain attached to the tree throughout the winter, then turn purple and drop from the branch the following spring. Most defoliation occurs late in the summer of the second year after infection and proceeds from the oldest, innermost, needles to the youngest and from the branches nearest the ground up. Affected branches are eventually defoliated and killed by the fungus.
Poor air circulation and high relative humidity favor the development of the Rhizosphaera fungus. So increasing air movement around trees is important.
Fungicide applications may be necessary to suppress further infection on diseased trees. And, proper timing is critical for control. Applications should be made just as new shoot growth is ½ to 1 inch long. We recommend a second application after 3 weeks. Call the Extension Office for a current list of fungicides that will control Rhizosphaera Needle Cast and are safe to use on blue spruce.