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Caption: Armillaria root rot infecting trunk
Photo by: C.R. Foss
  
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Rhododendron : Armillaria root rot
(revision date: 4/23/2014)


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

Non-Chemical Management
  • 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.
Select non-chemical management options as your first choice!

Chemical Management


None recommended

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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