Many spruce trees are showing dieback this year. According to Rhonda Ferree, extension educator in horticulture, the cold, wet spring has brought out many trees diseases. Many of these diseases are causing significant damage on evergreens throughout central Illinois.
The first spruce disease is 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 cast (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 cast while Colorado blue spruce is a common host.
Control recommendations for Rhizosphaera include 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 2 years of fungicide applications are usually required. If you suspect this disease, do not spray this year (2016) as it is too late. Instead, begin sprays in early 2017.
The second disease we see regularly on spruce in Illinois is Cytospora canker. That 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 (aka 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.
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.