Contact 888.969.8733

Armillaria Root Rot - tree disease associated with too much moisture

armillaria root rot - california tree diseases

Photos courtesy of Larry Costello PhD - University of California


Armillaria root and crown rot is most active when the soil is cool and moist. The pathogen survives in the soil on the roots of infected trees from one year to the next. In the absence of a living host, it can survive for several years on old infected roots or other woody material buried in the soil. The mycelium of the fungus grows up and down the root under the bark from the point of infection. It eventually reaches the crown where it girdles the tree and kills it.


Affected trees usually show a general decline in vigor over many years. Sometimes trees that look healthy will suddenly wilt and die in a matter of weeks. The above ground symptoms are similar to other root problems, including too much water, appearance of mushrooms or Phytopthora root rot. The key symptom to look for is to spot trees that are declining in patches and the patches seem to get larger each year.

Blowdown during rainstorms or winds are often the first and only indication of root rot. Sparse foliage with limb dieback also may be symptomatic of root rot. By scraping off the bark in small sections on the crown and main roots, it should be easy to see the dense, creamycolored plaques of mycelium between the bark and wood. Infected wood will have a strong mushroom smell and feel spongy. Dark brown to black rhizomorphs (structures that resemble shoestrings) sometimes can be seen on the root surface.

Arborwell Tree Services Wellness Approach

Exposing an infected root crown and upper root area of a tree infected with Armillaria mellea will stop the development of the fungus and allow the tree to regrow. Removal of the soil from around the base of the tree to a depth of nine to twelve inches and leaving the root flair exposed is critical. Keeping the upper roots and crown area as dry as possible will hinder rot. Prompt action upon diagnosis is important. Arborwell’s “Airspade” process insures minimal damage to existing roots.

Contact Us
To speak with an Arborwell Wellness Specialist, please call 888-969-8733. Our team of certified arborists are ready to help with all your arboricultural needs.

Pruning & Removals are not part of the Wellness programs.

Download a PDF about Armillaria Root Rot

Contact Arborwell today to schedule an Annual Property Inspection

Anthracnose | Aphids | Armillaria Root Rot | Bark Beetles | Tree and Plant Fertilization | Fireblight | Insect and Disease Management | Mycorrhizae Fungi Treatments | Oak Tree Care | Oak Worm | Fusarium Wilt - Palm Tree Care | Pitch Canker Disease | Powdery Mildew Disease | Scale Infestation | Tussock Moths |