Norway spruce trees are susceptible to a variety of fungal infections that often cause defoliation and discoloration of foliage. Keeping your tree as vigorous as possible through proper maintenance ensures greater potential for fighting off disease. Determine which disease your Norway spruce is affected by through observation of symptoms and always treat biologically before turning to chemical control; chemicals may cause excess damage to plant tissue beyond damage caused by the disease.
For preventive care in fighting the occurrence of Norway spruce diseases, keep your trees vigorous by growing them in full sun and moist, slightly acid, well-drained soil. Pay attention to the height expectancy of particular trees; though some Norway spruces come in dwarf varieties, standard trees may reach up to 60 feet tall with much more expansive root systems than small spruces. Allow enough room for proper growth. Plant Norway spruce trees in USDA Hardiness Zones 3 to 7, as recommended by the University of Illinois Extension HortAnswers.
Different fungal strains are responsible for a variety of diseases affecting Norway spruce trees. The fungus called Inonotus tomentosus causes tomentosus root rot. Spores of this fungal infection enter trees through root wounds. Spruce needle rust also infects Norway spruce trees, but to a less prevalent extent. Spruce needle rust forms due to the presence of several varieties of the fungus Chrysomyxa. Chrysomyxa attack less established needles during periods of cool temperatures and high moisture.
Symptoms and Damage
Tomentosus root rot is a disease that infects roots and trunks; this disease causes decay and pits in heartwood, stunted growth, sparse tree canopies, breakage during violent weather and the presence of mushrooms. Since the root system of Norway spruces usually die from tomentosus root rot, the rest of the tree's health declines and the entire tree may die. Symptoms of spruce needle rust include yellowed needle tips, needle drop or tubular orange to white growths on needles. Rust generally creates cosmetic problems without severe damage, according to the University of Minnesota Extension.
Always remove and destroy diseased plant parts and keep any type of cutting or pruning tools sanitized between cuts and from tree to tree to avoid transference of disease pathogens. Provide your tree with good circulation of air to prevent excess moisture that serves as a fungi breeding ground. Lay mulch around the Norway spruce's base to protect roots and trunk from wounds such as accidental incisions from mowing. For infected trees, completely remove the tree and replace with resistant trees.
Certain diseases cause severe infection and may be treated with fungicides. In order to determine the proper fungicide, remember it must clear up the appropriate infection and must be safe for use on Norway spruce trees. If you have trouble identifying the particular disease, contact an arborist for a professional diagnosis and plan for professional chemical control. When trees reach tall heights, it is often difficult to apply fungicides as the trees are too large to cover without commercial equipment. Unfortunately, many diseases cannot be treated with chemicals and simply need replacement. Though the fungal infection called Rhizosphaera needle cast only seldom affects Norway spruce trees, chemical control includes two treatments of the fungicide chlorothalonil for prevention of infection in growing needles.