Armillaria root rot is a fungal disease transmitted between plants by root contact. Armillaria is often found in newly cleared soils or ones which have been flooded. Symptoms typically include sudden or gradual slowing of growth, yellowish or undersized leaves, leaf drop, dieback of branches, or gumming (sticky, oozing sap). 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. Young, stressed trees are most susceptible to infection. Armillaria-infected trees have damaged root systems and are more likely to fall in high winds. It may also make trees more susceptible to insect attack.

Management Options

Non-Chemical Management

Remove infected plants, including roots larger than 1" in diameter.
Air-dry soil from infected site before replanting.
Provide proper culture to decrease stress and encourage vigorous, disease-resistant trees.
Plant only resistant plant species in infected areas (when possible). A list may be found in the PNW Plant Disease Management Handbook 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: Armillaria rhizomorphs Photo by: R.S. Byther
Caption: Cherry Armillaria root rot Photo by: R.S. Byther

WSU Extension

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