Spruce trees can fall victim to any number of fungal infections and invasion from parasitic plants or insect pests, and spruce diseases can affect the needles, branches, or trunk of the tree, while others begin destruction by invading the roots. Trees with needle cast diseases often exhibit symptoms within months after infections, but root diseases can survive in a tree for decades, slowly weakening the entire tree. Topical chemical sprays eradicate some types of spruce diseases, but others require eventual tree removal. Arborists are generally able to identify different types of spruce diseases and to recommend a course of action.
Fungal infestations are the most common infections observed in different types of spruce trees. Needles turn from yellow to brown, and, upon close inspection with a magnifying glass, tiny black spots become visible. Rizosphaera kalkhoffii for example, produces a condition known as needle cast, as the affected needles die and drop off the tree. In three to four years, affected branches are completely barren. Cryptospora canker invades the branches and moves toward the trunk, producing a white discoloration and a resin that runs down the tree.
The fungal infections caused by Inonotus tomentosus or Armillaria typically invade spruce trees at the root. The infected wood appears discolored and develops pockets of rot. These spruce diseases commonly produce mushrooms at the base of the tree. The opportunistic invaders destroy the tree slowly, surviving for 20 or 30 years, by depleting the host of nutrients and water. Root spruce diseases also diminish the strength and stability of the tree, which can cause even the largest of evergreens to topple during high winds or seasonal storms.
Maintaining tree health by properly caring for spruce trees may prevent extensive damage. Arborists suggest watering at ground level only, as the dense foliage of spruce trees has a tendency to hold moisture. When exposing needles and branches to water is inevitable, water during the early morning, allowing time for drying before nightfall. Specialists also advise adding 3 to 4 inches (7.5 to 10 cm) of mulch around the bottom of the tree for moisture retention and as a barrier against possible injury from lawn mowers. Birds, insects, rain, and wind often transport spores from one location to another, making exposure prevention highly unlikely.
The sticky seeds of the parasitic plant, Eastern spruce dwarf mistletoe, also travel from host to host through a wide variety of ways. Once in contact with a tree branch, the seed sprouts, sending root systems burrowing into the bark and depriving affected areas of food and water. The branch eventually develops visible sprouts, referred to as witch's brooms, which average less than one inch in height, and range from orange to brown in color. Flowering sprouts have the capacity to spread seeds dozens of feet (1 foot = 30 cm) away from the tree of origin. While homeowners can prune sprouts, infestation remains buried deep in the branches, eventually requiring complete tree removal.
Spruce diseases can also occur as a result of the presence to insect larvae. Various types of moths, spider mites, and wasps lay eggs on growing spruce trees. Larger insect infestations might appear as cocoons or webbed nests attached to needles and branches. When hatched, the larvae eat the buds or needles of the tree. A variety of liquid pesticides usually eliminates the infestation, sparing the tree from further damage.