Honey Fungus is a common name for the fungus disease Armillaria mellea. It is also known as oak root fungus, mushroom root rot and shoestring fungus. It is a soilborne disease that is known worldwide and affects both woody and herbaceous plants. The term honey fungus is derived from the color of the mushroom cap that emerges at the base of infected trees.
Armillaria tends to attack trees and pants whose health is already compromised. Often tree roots that are stressed by drought are susceptible to the fungus. Another sign the tree or shrub could be in danger is defoliation caused by insect infestation or other disease. Plants that have been injured, such as a wound to the bark, could also be in danger.
What Honey Fungus Does
The fungus lives in soil naturally. When the roots of the tree become stressed, the fungus begins attacking the roots, rotting them a little at a time. As the root system weakens, the tree is less able to assimilate water and soil nutrients and the overall health of the tree deteriorates. Occasionally, the tree will topple over as a result of the lack of a root support system.
Honey fungus has several phases that can be identified by different symptoms. Mycellium are whitish, leathery plaques that grow between the bark and the wood either at or below ground level. It begins in one or more roots and spreads to the wood. The mycellium smell like mushrooms as does infected wood that has become soft.
Rhizomorphs are where the term shoestring fungus comes from. Though not always present, they are black, cord-like structures that may appear under the bark and on the roots. They penetrate the bark and infect the woody tissue beneath. Rhizomorphs are the predominate means by which the disease spreads from one infected root to another tree. They have been known to grow 3 to 8 feet in the soil.
Mushrooms are the fruiting stage of armillaria. Honey fungus takes its name from this phase as the mushrooms, when present, are honey-colored. Usually in clusters, the mushrooms appear on the exposed woody roots or the lower trunk of the tree. They can range anywhere from to 2 to 5 inches in diameter and can be 4 to 5 inches in height. Mushrooms appear at different times in different parts of the country but generally from autumn to winter depending on the climate.
There is no known treatment that is effective at eradicating the disease. Maintaining good tree and shrub health is the best prevention against honey fungus as it only invades tissue already weakened by something else. Maintain a good fertilization and watering regimen. Plant disease-resistant trees in suitable soil and remove dead stumps and root systems to prevent spread. Don't plant in locations where the disease is known to have been active as it can remain viable in the soil for many years.