Cedar trees are susceptible to various diseases. The two most common types of cedar trees, Western Red Cedar and Eastern White Cedar, are often affected by root diseases and fungal infections such as root rot, Phytophthora disease, and cedar-apple rust.
Root rot, most commonly armillaria root rot, is frequently found in both red and white cedar trees. There is no cure and the disease is lethal to the tree. Root rot can be detected by the observation of white fungus, which spreads under the bark. This fungal mycelium is most commonly found towards the base of the tree or in the roots. The fungus will travel through the roots to neighboring trees and eventually kill all affected trees.
Phytophthora disease has many different strains that affect many plant species. The type that most commonly affects cedar trees is also known as phytophthora lateralis, or Port-Orford-Cedar Root Disease. A cedar damaged by this disease will have roots that appear to be wet, as the roots take on a very dark color. Western Red Cedars are resistant to this disease but Eastern White Cedars are highly susceptible. Phytophthora disease often attacks trees recently damaged by drought or flood.
Cedar-apple rust is commonly found in red cedar trees, such as the Western Red Cedar. This disease is caused by the Gymnosparangium-juniperi-virginianae fungus, which causes the tree to become covered in galls, or cedar apples. These galls appear as round to kidney-shaped growths that range in color from green-brown to deep brown. In rainy weather, the growths can become covered in yellow-orange jelly horns, or spores, up to two inches long. One gall can produce billions of spores that infect the tree, spreading the fungus throughout the plant. Usually, young leaves are the first portions of the tree to be attacked.