Spruce trees are coniferous evergreens. There are about 35 species of the tree worldwide, some of which are popularly used as Christmas trees. Spruce tree diseases can be classified as needle, branch or root diseases. The diseases can vary in severity, with some only disfiguring the spruce tree, and others eventually killing the tree. While some of the diseases are treatable, others are only preventable
Rhizosphaera Needle Cast
Rhizosphaera needle cast is a fungal disease that attacks the needles of the spruce. Colorado blue spruce is especially susceptible to this disease. The fungus that causes the disease is called Rhizosphaera kalkhoffii, and it is spread through splashing water--usually rain.
The disease causes the needles of the tree to slowly turn yellow, moving from the inner parts of the tree outward. The disease typically starts in the summer and, over the course of a year, the needles will turn a darker brown and fall off the tree, leaving it with a thin, spindly appearance. Because new needles are only produced on the tips of the branches of coniferous trees, the lost needles will not be replaced with new growth. Over time, the spruce tree will most likely die.
Rhizosphaera needle cast cannot be treated once it takes hold of a spruce tree. However, new needle growth can be protected with two applications of chlorothalonil in the spring. Prevention includes careful watering of young trees (avoid watering from above) and planting resistant species of spruce, such as the Norway spruce
Spruce Needle Rush
Spruce needle rust is a fungal disease that attacks the needles of white, blue and black spruce trees. Unlike the rhizosphaera fungus, this fungus attacks the new needle growth on the tree, turning needles yellow. In midsummer, fungal bodies will develop on the yellow needles. These tiny, orange or cream protrusions hold new fungal spores, which release into the wind in the fall. Afterward, the yellowed needles fall off.
This fungal disease does not harm the spruce. It is only a cosmetic problem and is not treated with any chemical means, although the tips of the branches can be sheared off to improve the appearance of the tree.
Cytospora canker is caused by the Leucostoma kunzei fungus. This disease infects the branches of the tree, and sometimes even the trunk. Cytospora canker enters the tree from a wound caused by stress--frost damage, other illness, or anything else that will split the wood--which is why it is usually older trees (more than 10 years old) that are infected.
When the disease infects the tree, it causes the branches to begin to die from the tips inward. The sap becomes infected and oozes out of the tree, and the needles turn brown and drop off. Pruning away infected areas is the only way to control the disease and prevent it from spreading to the rest of the spruce. This often leaves the spruce tree with an unsightly appearance.
Tomentosus Root Rot
Tomentosus root rot is caused by the fungus Inonotus tomentosus. This soil-based fungus attacks the roots of the tree; most often, the roots of black, white and Colorado blue spruce trees. From the roots, the fungus works its way up the heartwood of the tree, rotting it from the inside out.
Spruce trees that are infected with tomentosus root rot often have poor growth and thin crowns. They also produce excessive amounts of pine cones. Mushrooms often appear at the base of the tree, and because the spruces are rotten, they break easily in storms or strong winds. Eventually, the tree will die. There is no treatment other than to avoid planting saplings in areas where the disease has been known to occur.