Blue spruce trees (Picea pungens), also called Colorado spruce and Colorado blue spruce, are coniferous trees native to the Rocky Mountains. They usually grow between 50 and 100 feet tall, with pyramidal or open crowns and silvery-blue or green needles. They are a slow-growing but long-living species, with lifespans up to 600 years, and they are often used as cultivated ornamental trees. Blue spruces are susceptible to a variety of diseases, pests and problems.
Needle Cast and Rust Diseases
The Rhizosphaera kalkhoffii fungus causes rhizosphaera needle cast. This is the most common disease in blue spruce trees, according to the Iowa State University Extension. The fungus spends the winter in diseased needles and becomes active during the spring. It spreads to new needles through splashing water. Infected needles turn purplish-brown, yellow or red; the discoloured needles may fall from the tree or stay on the branches throughout the winter. Severe rhizosphaera infections cause branch dieback or eventual tree death. Several types of rust diseases (Chrysomyxa sp.) also cause needle loss and damage blue spruce cones.
The Cytospora kunzii fungus causes cytospora canker infections. This fungus usually affects large, mature blue spruce trees, but it can infect trees of any age. The fungus enters the tree through mechanical injuries or other wounds and creates sunken areas of diseased bark called cankers. Infected trees exude a white, glue-like sap and infected branches die. The Leucostoma kunzei fungus causes leucostoma canker. Branches near the base of the tree turn greenish-grey or brown and die first; the disease gradually travels upward and spreads throughout the crown.
Several fungi, including Intotomus tomentosus, Armillaria mellea and Cylindrocladium scoparium, cause root rot infections in blue spruce trees, while Phytophthora cinnamoni causes damping off, a disease that kills blue spruce seedlings. Phomopsis occulta causes tip blight, nematodes infect the roots, and western spruce dwarf mistletoe infects and kills blue spruces. Young cultivated trees may lose branches or die within their first year if they are not watered regularly.
Green spruce aphids feed on blue spruce tree twigs. Larval budworms feed on the buds and needles, while spruce coneworm larvae burrow into the cones and feed on new foliage. Pine leaf aphids and Cooley spruce gall aphids create deformed, raised areas of plant tissue called galls. Several types of beetles such as ambrosia, spruce and twig beetles also feed on different parts of the tree, depending on the species. Other pests include pine needle scale, spruce needle miners and yellow-headed spruce sawflies.