Blue Spruce Diseases

A cherished conifer found in many landscapes is the Colorado blue spruce (Picea pungens 'Glauca'), State Tree of Colorado and Utah, and native to the Southwestern United States (Zones 3–7). It is commonly planted in Pennsylvania for its bluish-green foliage and conical shape. Selections of Colorado spruce include dwarf, weeping, and prostrate forms, as well as those selected for intense silvery-blue needles.

Spruce trees can be distinguished from other conifers by their single, four-sided needles which are rigid and very prickly. Picea pungens has a symmetrical, pyramidal shape and grows 30 to 60 feet tall and 10 to 20 feet wide. It prefers moist but well-drained soil, full sun, and good air circulation.

Spruce often tends to lose lower branches and become unattractive with age, especially during periods of environmental stress caused by drought and frequent rain.  Recent wet weather years have been especially hard on spruce trees, as evidenced by the number of dying trees visible in local landscapes.

A common fungal disease, Cytospora canker, generally affects older blue spruce trees but may also infect Norway spruce.  Cytospora is a canker disease that starts in lower branches and spreads upwards. Inconspicuous cankers develop on lower branches—the cankers girdle the branches, causing resin to flow out of the cankers and drip down the trunk of the tree. Needles brown and drop, and eventually, entire branches die back to the trunk.  Thousands of fungal spores develop in the canker and are transferred to other branches during wet weather, and the disease spreads upward throughout the tree. Wet spring weather is an ideal condition for cytospora to spread. While fungicide sprays cannot be timed to effectively control the disease, dead branches should be removed in late winter or during dry weather. Disinfest pruning tools between cuts to avoid spreading the disease. In time, trees will become unsightly and should be removed.

Another fungal disease affecting spruces is Rhizosphaera needlecast. Symptoms may first appear in mid- to late-summer as yellowing of the innermost needles on the middle to lower sections of the tree. These needles change from yellow to brown or purplish-brown and eventually fall off the tree. Like Cytospera, this fungus is also spread during wet weather and may also infect Serbian spruce, mugo, and white pines. Specialty cultivars of blue spruce are also susceptible to Rhizosphaera needlecast.

Fungal black fruiting bodies may be seen on the underside of needles with a 10X hand lens. Control of fungal disease is difficult because infection extends from spring through autumn, depending on rainfall. Infected branches remain on trees as a source of infection for several years with progression of disease. Preventive fungicides containing copper or chlorothalonil may be applied in spring to protect new growth, but will not cure infected needles. Infected branches can be removed, making sure tools are disinfested between cuts. Severely infected trees should be replaced. For large trees, contact a professional arborist.

Because of susceptibility to these diseases, less vulnerable conifers including concolor fir (Abies concolor), Oriental spruce (Picea orientalis), Serbian spruce (Picea omorika), and cultivars of Eastern red-cedar (Juniperus virginiana) should be used in preference to Colorado blue spruce. All are hardy in our region.