Spruces (Picea spp.) are large trees with ridged evergreen needles. Most varieties grow up to 40 feet tall, but some dwarf varieties are shorter. Younger trees have a pyramidal shape that opens up as they mature. The color of the needles on spruce trees varies from light to dark green and from bluish to silvery, depending on the variety. The cones range in size from 1 to 6 inches long. Spruces prefer well-drained, moist soil but will adapt to other types of soil. They do grow well in hot, dry conditions. Only a few diseases bother spruce trees.
Foliage diseases of spruces are seldom fatal, but they can affect the tree's appearance and growth. Several types of fungi cause spruce needle rust on new growth, causing it to turn yellow. Then whitish to orange tube-like projections grow on the infected needles, releasing powdery orange spores in the late summer, causing the needles to fall off the tree. Lirula needle blight affects needles of all ages. The needles will develop yellowish bands that turn purplish-brown. The color spreads over entire infected needle. Rhizosphaera needle cast is a common disease of spruce trees and affects all ages of needles. They first turn yellow, then purplish-brown and finally fall off. Needle blight and needle cast can be treated with a fungicide approved for fungal diseases on spruce trees.
The Cytospora fungus causes the bark to decay and form cankers. Eventually foliage and limbs will die, particularly near the bottom of the tree. Bluish resin oozes from the diseased areas and black fruiting bodies grow under the infected bark. Remove and destroy infected branches in the winter. Infected branches are dull-colored or grayish green, and dead branches are brown.
Root rots are fatal to spruce trees. The trees and all the roots should be removed and destroyed to prevent the spread of infection. The symptoms of Armillaria root rot are brown needles, dead branches and overall poor growth. Honey-colored fruiting bodies (mushrooms) grow around the base of an infected tree in the fall and white sheets of fungal mycelia grow under the infected bark. In some cases, thick fungus strands form nets on infected trees and ground. The heartwood of the roots and trunk of a spruce infected with tomentosus root rot turns reddish brown and develops pockets or pits of rot. The tree loses vigor and the canopy thins. Velvety brown fruiting bodies grow around the base of an infected tree in the summer.