Cedar root fungus is caused by Phytophthora lateralis. It affects cedars that are nursery stock, timber trees and ornamentals. Cedar root fungus was first seen on ornamental cedars in 1923, near Seattle, but it was not named until 1942, when the fungal cause was discovered in Willamette Valley in Oregon.
Infected roots look like they are water-soaked at first. As the disease takes over, the roots darken. Finer roots start to disintegrate and the cambium and inner bark on larger roots turn deep brown. The healthy inner bark remains a creamy color.
Cedar Root Fungus Spread
The disease starts to spread through the tree, affecting a portion of the trunk that is about twice the stem diameter. Foliage is lighter in color, then it withers, turning bronze then light brown. The crown of the tree eventually dies. Bark beetles attack the trees. When the bark beetles move to another tree, they carry the disease with them, spreading cedar root disease to healthy trees. The disease is also spread by moving dirt from one spot to another (i.e. in tracking infected soil from one area to another on equipment wheels).
Port-Orford cedars were almost completely wiped out due to the fungus. Residents who used the Port-Orford cedars in their landscaping had to have the dead trees removed. This cost the residents to have the trees removed, caused aesthetic losses due to property devaluation, and warranted costs to replace the trees. Commercial forestry also took a loss because of the disease. Younger trees are barely usable. Older trees die within two to four years of being infected with Cedar root disease.
Fungicides can be used in residential yards to prevent Cedar root disease, but have limited use in the forest. Some fungicides do not eliminate the fungus, but mask the presence of the fungus, thereby increasing the risk of transferring the disease to new planting sites. The disease is not airborne, so new stock is planted on elevated ground that is disease-free. Sources of the disease should be eliminated or otherwise controlled. Isolate the source of infection to keep the fungus from spreading.
The disease is spread through pests, contaminated soil and contaminated water. Keep planting sites sanitary. If you are not sure whether an area is contaminated, clean up (change shoes and clothing, wash your hands) before tending to the trees in a known healthy spot. Create upper and lateral boundaries around the trees to keep affected surface water from running down into trees and infecting them. Wash equipment prior to bringing it near known, healthy trees. Do not choose a low spot to plant the cedars. Keep them at least 50 feet from water.