Armillaria Root Rot Of Trees
Plants most susceptible to Armillaria root rot are those under stress from prolonged drought, repeated insect defoliation, root injury, or recent transplanting.
Armillaria survives well in dead roots and stumps and in the soil as long, brown, shoestring-like structures. These rhizomorphs (root-like structures) can grow for several feet through soil from stumps to nearby trees and from tree to tree. This is very unusual for a fungus since most fungi remain relatively dormant in soil unless a host plant is very near. The rhizomorph invades a tree at the buttress or upper part of the root system. Just under the bark, obvious white fans of fungal growth form. A honey-brown colored mushroom develops in the autumn on the roots or buttress of infected trees. The spores liberated from the mushroom are windblown to other areas.
Top growth of the infected tree slows, branch dieback occurs, and roots rot. Trees may appear to die quickly. White fans of fungal growth are found when bark is peeled off infected trunks near the soil line. Conifers have abundant resin flow from the trunk at the soil line.
Encourage Good Tree Vigor By Reducing Stress Including:
- Control insects that cause defoliation.
- Irrigate to relieve drought.
- Protect plants against injuries to the lower trunk and upper portion of the root system.
- Do not replace an Armillaria-killed plant with another woody species.
Rhizomorphs of Armillaria
Armillaria mycelial fan.
Prepared by Gary W. Moorman, Professor of Plant Pathology
Notice: The user of this information assumes all risks for personal injury or property damage.
Warning! Pesticides are poisonous. Read and follow all directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams or ponds.
Issued in furtherance of Cooperative Extension work, Acts of Congress, May 8 and June 30, 1914, in cooperation with the U. S. Department of Penn State College of Agricultural Sciences research and extension programs are funded in part by Pennsylvania counties, the Commonwealth of Pennsylvania, and the U.S. Department of Agriculture.
Visit Penn State Extension on the web at extension.psu.edu.
Where trade names appear, no discrimination is intended, and no endorsement by Penn State Cooperative Extension is implied.
This publication is available in alternative media on request.
The Pennsylvania State University is committed to the policy that all persons shall have equal access to programs, facilities, admission, and employment without regard to personal characteristics not related to ability, performance, or qualifications as determined by University policy or by state or federal authorities. It is the policy of the University to maintain an academic and work environment free of discrimination, including harassment. The Pennsylvania State University prohibits discrimination and harassment against any person because of age, ancestry, color, disability or handicap, national origin, race, religious creed, sex, sexual orientation, gender identity, or veteran status. Discrimination or harassment against faculty, staff, or students will not be tolerated at The Pennsylvania State University. Direct all inquiries regarding the nondiscrimination policy to the Affirmative Action Director, The Pennsylvania State University, 328 Boucke Building, University Park, PA 16802-5901; Tel 814-865-4700/V, 814-863-1150/TTY.