Conifers are woody-stemmed, cone-bearing perennials, which means they bear seed in cones. Conifers also tend to be evergreen and retain their leaves through the year. Common conifers include cedars, cypresses, firs, junipers, larches, pines, redwoods and spruces. Most types are hardy, long-lived plants, but some are susceptible to coniferous diseases that may affect the foliage, branches, stems or roots, according to the U.S. Forestry Service's Forest Health Protection Division.
Needle cast is a fungus that affects firs, pines and spruce. The disease can kill saplings, but usually only causes pronounced needle loss. The first sign of infection appears in winter when new needles form yellow or brown spots. The fungi produce black-fruiting bodies at the center of the spots, which eventually gives the tree a scorched look. The disease spreads when the fruiting bodies release spores in spring. Rain water falls on infected needles and splashes to infect additional needles. Apply fungicide spray to control the spread and prune dead and infected branches in winter.
Fusiform rust is one of the most serious fungus-caused diseases to kill, deform or severely weaken pines in the southern portion of the U.S. The disease affects saplings or trees under 8 years old. Fusiform rust requires an alternate host, like an oak tree, to complete the life cycle. Diseased trees display orange spores in spring. Other symptoms include galls, abnormal growths, and witches broom--a point on the tree that shoots multiple twigs. Plant pines that are resistant to rust, such as pitch, pond, longleaf and shortleaf pines, according to the University of Mississippi Extension's publication, "Southern Fusiform Disease." Remove infected trees that look like they could be stem-breakage hazards.
Armillaria root disease is a fungal disease that kills hundreds of species of shrubs, vine and trees in all 50 states--but it is especially active in inland coniferous forests of the western U.S. The disease spreads from tree to tree from filament clusters known as mycelia and root-like structures called rhizomorphs, both of which are in the soil.
Over time, infected coniferous trees shows signs of stress. The needles thin and turn yellow, then red or brown. Branches suffer dieback and the lower stems produce large quantities of resin. Fumigants may reduce infection when applied to the base of infected stems. Remove roots and stumps of trees that were once infected with armilleria root disease because they will continue to serve as a food source for the fungus.