When dreaming of a picturesque winter landscape, the spruce genus (Picea spp.) may come to mind. Spruces are evergreen shrubs and trees that generally thrive in cool conditions, retaining their green or bluish needles year-round. A diseased spruce however does little to improve the scenery. Following proper preventive measures is always preferable to treating a disease.
In compacted, wet soil, spruce may fall prey to root, crown, collar or foot rot caused by various species of Phytophthora fungi. Symptoms may include wilted, discolored needles, twig and branch dieback and needle drop. The trunk may develop a dark, rotten patch or streak, and infected areas might secrete sap. Prevent rot by planting spruce trees only in well-draining soil in areas not prone to flooding. Avoid planting spruce in areas where rot has been a problem.
A host of pathogens may cause damage to the spruce's needles, including needle cast fungi, needle rust and Stigmina needle blight. Needle cast causes brown or black lesions on needles and occasionally canker and branch dieback, while needle rust causes older needles to turn brownish-orange. Needle blight also causes rust-like coloring on older needles, though black fruiting structures may also be present. Prune out infected needles, sterilizing your pruning equipment afterward with rubbing alcohol to avoid spreading pathogens, and remove weeds, which inhibit air circulation. In severe cases of rust disease, Penn State Extension recommends destroying the tree.
Cytospora canker is more likely to attack spruce trees stressed from environmental factors such as drought and winter injury, as well as trees 10 years or older, according to the University of Minnesota Extension. Symptoms include crusty white or bluish cankers on infected branches, girdled branches and brown or purplish needles. Keep the tree well-irrigated to reduce stress. Rainy weather can spread the disease, so prune infected branches only when the weather is dry and destroy them afterward.
Prevent and Prosper
Good cultural care from the beginning can help prevent disease and provide your tree with a strong, healthy foundation to fight any diseases that do take hold. Plant spruce trees only where they are hardy. Both blue spruce (Picea pungens), also known as Colorado spruce, and Norway spruce (Picea abies) are hardy in U.S. Department of Agriculture plant hardiness zones 3 to 8, where they prefer full sun and moist, well-draining soil. Mulch with a 2-inch layer of organic material to help retain moisture in the soil. Space trees at least 6 to 13 feet apart to allow air to circulate.