Root Rot

Root rot is a general term for diseases that decay the root system of trees. Major root rot pathogens include Armillaria species (honey fungus), Phytophthora species (water molds), Ganoderma species, and Heterobasidion annosum (in conifers). These organisms attack fine absorbing roots, structural roots, or both, compromising the tree's ability to take up water and nutrients and to remain anchored in the soil.

Symptoms of root rot develop gradually and are often mistaken for other problems. Affected trees show general decline with thinning canopy, small or chlorotic leaves, premature leaf drop, and reduced growth. As structural roots decay, the tree may lean or show soil cracking at the base. Fruiting bodies such as mushrooms or bracket fungi at the base of the tree are often the most definitive visible indicator of root rot.

Root rot is particularly dangerous because it can cause catastrophic tree failure with little warning. A tree with extensive root decay can topple in moderate wind, potentially causing serious property damage or injury. Diagnosis should involve careful investigation of the root flare and buttress roots. Management options are limited once root rot is established; prevention through avoiding soil compaction, excessive irrigation, and root damage is far more effective than treatment. Severely compromised trees should be assessed by a qualified arborist and may require removal.