Armillaria root rot is a fungal disease often found in newly cleared soils or soils which have been flooded. Aboveground symptoms typically include production of smaller-than-normal leaves, leaf yellowing, premature leaf drop, and branch dieback, often on only a portion of the tree. White thread-like masses of the fungus may be found beneath the bark near the crown of infected trees, and/or as shoestring-like rhizomorphs, which are dark strands of the fungus growing on or just beneath the soil surface. Honey-colored mushrooms often grow near the base of infected trees in the fall. Infected trees may also exhibit a dark black line in the infected area encircling the base of the plant. Trees damaged by human activity such as construction or improper irrigation are more susceptible.

Management Options

Non-Chemical Management

Use resistant rootstocks. Mazzard rootstocks are reported to be moderately resistant after they are well established.
Provide proper culture. Healthy plants are more resistant to infection.
Remove damaged trees if necessary. When possible, remove roots 1" or more in diameter and air-dry soil before replanting.
Avoid injury to roots and trunk.
Plant resistant species in infected areas. Lists are available in the PNW Plant Disease Management Handbook and the Sunset Western Garden Book, or contact your county Extension agent or WSU Master Gardeners.

Select non-chemical management options as your first choice!

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides

None recommended

Images

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Caption: Armillaria root rot infecting trunk Photo by: C.R. Foss
Caption: Armillaria root rot infecting trunk Photo by: R.S. Byther
Caption: Cherry Armillaria root rot Photo by: R.S. Byther
Caption: Armillaria rhizomorphs Photo by: R.S. Byther

WSU Extension

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