Spruce trees (Picea sp.) are coniferous evergreens. There are 12 species of spruce trees worldwide, according to the United States Department of Agriculture. These medium-to-large sized trees usually attain heights of over 40 feet (some are as tall as 100 feet or more, such as the Norway spruce) and are often favored for use as Christmas trees. There are three primary diseases that attack spruce trees. Of these, one is relatively rare.
Rhizosphaera needlecast is caused by the fungus Rhizosphaera kalkhoffi. This fungus travels on water, usually rain that is blown onto the spruce from another tree. For this reason, infections often arise during unusually wet spring weather. The fungal spores sit on the needles and infect their breathing pores. Symptoms of this disease first appear on the inner part of the lower branches of the spruce tree, where the needles will turn brown and fall off. Eventually, the disease moves up the tree, giving the spruce a rather bald appearance, as the outer tips of the branches are often still covered with fresh, new green growth.
If the fungal disease is not treated, the tree will eventually die. The only treatment is application of a fungicide that includes chlorothalonil. Spray the tree thoroughly when new growth is about one inch long, then again two weeks after the first application. Make sure all affected branches, as well as those below and above, are covered with the fungicide. Repeat the two applications each year for two consecutive years to rid your spruce of the disease.
Cytospora Canker Disease
Cytospora canker is a disease signified by the development of cankers in the wood of the spruce tree. It is caused by the fungus Cytospora kunzei. The fungus enters the wood of the tree through a wound such as those caused by pruning or a lawn mower blade, or on the body of a boring insect. The infected wood becomes dead, cracked and discolored. Often, silvery or white sap oozes from the cankers. The infection also cuts off the flow of water and nutrients to that part of the tree. This results in dieback--the tree beginning to die from the outermost parts inward.
Unfortunately, there are no fungicides that can prevent or treat this disease. Infected branches should be immediately pruned off to prevent the spread of the fungus. Dip the pruning tools in bleach to sterilize them and kill any clinging fungal spores between cuts.
Rust diseases, which are often seen in broad-leafed, deciduous trees, sometimes also infect needled, coniferous trees, including spruce trees. The fungi that cause rust disease travel on water, such as blowing rain. The fungus infects the needles of the tree, turning them yellow and causing them to drop off. Rust diseases can be prevented with a copper spray in early spring, but because they are so rare on spruce trees, most home gardeners focus on preventing other, more common diseases.