Example of black, shoestring-like rhizomorphs on a rotting stump

ARMILLARIA ROOT ROT - Armillaria mellea is called shoestring fungus (named for the shoestring-like rhizomorphs), or honey fungus (named for the mushroom fruiting bodies the fungus may produce). It can infect hundreds of plant species but mainly it attacks woody plants. This pathogen usually attacks trees suffering from other stresses such as defoliation, drought, poor soil, and other diseases.  The symptoms are similar to the above ground signs of a failed root system.  The infected plant's growth slows, foliage may become off-color, less dense or undersized, foliage may drop early, and branches die.  Eventually the entire tree will be killed, but this usually takes several years.  Small trees or shrubs often die quickly, but large ones may be chronically diseased as they slowly suffer growth loss and decay of roots.  These plagued large trees can become potential hazards as they are subject to windthrow.  It is possible for a larger tree to survive for awhile as it can slow the armillaria by blocking the pathogen from spreading (compartmentalizing the pathogen). Infected trees will have a white to tan colored mat of fungus beneath the bark at the root collar (trunk base).  Also, black shoestring-like fungus parts will form on diseased roots and creep up the root collar.  These shoestring-like fungus parts are called rhizomorphs and they act like the roots of the fungus by spreading it about one or many host plants.  Sometimes several years after the infection, honey-colored mushrooms will form at the base of the diseased tree.There is no way to control the fungus except to help the plant keep its vigor through good horticultural practices.  If the diseased tree is taken down, the stump should be fully removed.  The reason for making sure the infected tree stump and tree are cleared is because the fungus will continue to feed on the decaying wood.  As the fungus runs out of food, it will have built-up strength and may move through the soil to find another victim.  The fungus can persist for decades in decaying wood and soil.