Rhododendron: Armillaria root rot

Biology

Armillaria root rot is a fungal disease transmitted between plants by root contact. Armillaria is often found in newly cleared soils or soils which have been flooded. Symptoms typically include production of smaller-than-normal leaves, leaf yellowing, leaf drop, and dieback of branches. 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. Armillaria is also known as oak root fungus.

Management Options

Use Integrated Pest Management (IPM) for successful plant problem management.

Non-chemical Management

Select non-chemical management options as your first choice!

• Remove infected plants, including roots.
• Air-dry soil from infected site before replanting.
• Proper irrigation reduces the likelihood of Armillaria infection.
• Plant only resistant plants in infected areas. A list may be found in the Sunset Western Garden Book, or contact your county Extension agent or WSU Master Gardeners.

Chemical Management

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

• None recommended

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