Treatment of Spruce Tree Diseases

Cytospora Canker Treatment

• Cytospora canker is a fungal disease that infects spruce trees and can eventually kill them. Needles will change to brown and fall from the tree. Lower branches die first as the disease progresses. Pale blue or white resin spots and cankers will become evident on bigger branches after they die. Treatment with fungicide is not recommended for this disease. Infected branches must be pruned off completely and either removed from the property or burned. Pruning should be done later in the winter on a sunny day when the tree branches are dry. Clean and disinfect the loppers or pruning saw with a bleach solution diluted at a rate of 9 parts water to 1 part bleach. Give the tree 5 to 6 gallons of water for every 10 feet of tree width every 10 days to two weeks during droughts to keep the tree healthier and better able to withstand this disease. In the fall, four weeks after the first hard frost, measure the width of the tree trunk 4 feet up from the soil and sprinkle 1 pound of 16-4-8 or 12-4-8 fertilizer per inch of trunk width around the tree. The fertilizer can help the spruce survive.

Rhizosphaera Needlecast Treatment

• Rhizosphaera needlecast is a fungal disease that causes symptoms similar to cytospora canker, but this disease does not usually kill the entire tree. The needles develop spots or mottling and may turn yellow or purple-brown later in the summer. They change to brown late in the winter or early in the spring before dropping in the summer or fall. The branches do not develop resin spots, but small black spores form on the needles. Like cytospora canker, the diseased branches should be pruned and the spruce should be watered regularly and given fertilizer in the fall. Avoid wetting the needles and branches. Unlike cytospora canker, this fungus should be treated with a copper fungicide if the disease is severe. Copper fungicides are sold pre-mixed in spray bottles, but they are also sold in concentrated form, powder form and dust form. Apply the fungicide, thoroughly coating the needles and stems, when the needles are half their mature length and again when they reach full length. The treatment must be applied for at least two years. Be very cautious when applying the fungicide. Follow the manufacturer’s instructions and precautions.

Stem and Needle Rust Treatment

• While not a common spruce disease, stem and needle rust can attack some types of spruce. “Densata” white spruce (Picea glauca “Densata”), for example, is susceptible to this type of rust. Infected trees develop yellow spots on their needles in the fall and winter. The tell-tale rusty-orange spores develop during the following spring and summer. This fungus requires a nearby alternate host, usually goldenrod (Solidago spp.) or aster (Aster spp.), both commonly hardy in USDA zones 3 to 9. While the fungus is unsightly and the tree may lose its lower branches, it is not a serious threat to the spruce. Removing the asters or goldenrod plants should break the fungus life cycle and eliminate the disease.

Spruce Broom Rust Treatment

• Engelmann spruce (Picea engelmannii), hardy in USDA zones 2 through 5, Norway spruce (Picea abies), hardy in USDA zones 2 through 7, red spruce (Picea rubens), hardy in USDA zones 2 through 5, Sitka spruce (Picea sitchensis), hardy in USDA zones 6 through 8 and white spruce (Picea glauca), hardy in USDA zones 3 through 6 are susceptible to spruce broom rust. This is a fungal disease that causes witches’ broom or excessive, deformed twig formation at the branch tips that turn orange from the fungus. The alternate host is bearberry (Arctostaphylos uva-ursi), which is hardy in USDA zones 2 to 7. Prune off the diseased branches to limit the spread of the fungus and remove the bearberry to break the fungus life cycle.