Florida Forest Diseases
Armillaria root rot
Armillaria root rot (a.k.a. shoestring root rot or honey mushroom) is caused by a mushroom producing fungus (Armillaria spp.) that feeds on dead and living roots and woody debris in soils. It moves from tree to tree by two ways. First, mushrooms are produced at the base and on roots of diseased trees during the fall and winter, the spores produced by these mushrooms are airborne and cause new infections through stumps, wounds and exposed roots. Second, once the fungus has infected a host, it can produce black root-like structures known as rhizomorphs that move through the soil in search of new hosts. Usually, trees stressed by drought, flooding, insects and other diseases are affected most by armillaria. In Florida, oak trees (especially laurel oaks) are particularly susceptible. |
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Identifying Characteristics |
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Identifying the injury: |
Trees have thin crowns, may have wilting branches, dieback and loss of vigor; death. Roots are often rotted and poorly developed causing trees to lean. |
Identifying the fungus: |
The fruiting bodies (mushrooms) are yellow-brown and produced in clusters near the base or on roots of affected trees in cooler, wetter weather. Rhizomorphs may be seen on affected roots and stumps or in soil – look for black “shoe-string”- like masses on dead wood. Fungal tissue (mycelium) is white and occurs under the bark. It sometimes “glows in the dark” (bioluminescence) |
Susceptible trees: |
Many species – oaks and sweetgums are common hosts in Florida. Stressed trees are most likely to be affected. |
Photos |
Oak killed by armillaria Rhizomorphs of armillaria
Photo credit: Dr. Jason Smith, UF, SFRC Photo credit: Dr. Ed Barnard, FL DOF/DOACS
Fungal mycelia fan of armillaria
Photo credit: Dr. Ed Barnard, FL DOF/DOACS