According to Rhonda Ferree, University of Illinois Extension horticulture educator, spruce trees are experiencing three different diseases, each with slightly different symptoms and treatment.
Rhizosphaera needle cast: Spruce trees with purple/brown one- and two-year-old needles are suspect. The newest growth will appear green. Affected needles are dropped. Since evergreens do not re-foliate along the branches, the disease will cause bare areas scattered throughout the tree if untreated. Norway spruces are considered resistant to this needle drop while Colorado blue spruce is a common host.
To control the disease, Ferree recommends raking and disposing of infected needles that carry the disease pathogen. Infected trees can by sprayed with chlorothalonil in the spring when needles are half-grown and again when they are fully elongated. Chemical controls are affected if the disease is caught early. At least two years of fungicide applications are usually required.
"If you suspect this disease, do not spray this year as it is too late. Instead, begin sprays in early 2012," Ferree said.
Cytospora canke:This disease causes entire branches to turn purple/brown. Cytospora affects all needles from the tip of the branch to the base. Often lower branches are affected first. The disease may progress up the tree slowly, killing branches over a number of years. Cytospora or Leucostoma canker will occur on young trees, but it is more common on trees at least 15 years old. On spruce there is usually a sappy exudate associated with the canker, but this sap is a thin layer, not the large blobs of sap associated with some insect pests such as pine bark and pitch moths. The wood under the bark of a tree with Cytospora canker is brown (dead) rather than green or white. The fungus is known as a stress pathogen, meaning it invades spruce trees growing in less than ideal sites or environmental conditions.
Control recommendations for Cytospora canker include pruning and destroying dead and dying limbs during dry weather. Reduce tree stress by mulching around the tree and fertilizing in the fall. Too much or too little soil moisture is also a source of stress. There are no chemical controls for this disease.
Ferree said the third problem for spruce has been recently confirmed by the U of I plant clinic as a new spruce disease in Illinois called Sudden Needle Drop or SNEED.
"While SNEED has been found in several surrounding states, this is a first find in Illinois," Ferree said. "SNEED has been found on Norway, white and Colorado blue spruce trees."
The symptoms of SNEED are yellowing and eventual browning of older needles. Typically, by the end of summer, all of the needles on affected branches fall off except the newest needles on the tips of the branches. There are no control recommendations at this time for this disease.
For more information on these diseases and more, read the Home, Yard, and Garden Newsletter from University of Illinois Extension at http://hyg.ipm.illinois.edu/index.php, or by contacting your local Extension office at www.extension.illinois.edu. Ferree welcomes questions on her Facebook page at www.facebook.com/ferree.horticulture.