WSU Extension

Hortsense

Caption: Armillaria root rot infecting trunk
Photo by: C.R. Foss
  
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True Fir : 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 sudden or gradual slowing of growth, yellowish or undersized needles, needle loss, or 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. Young, stressed trees are most susceptible to infection. Armillaria-infected trees have damaged root systems and are more likely to fall in high winds. Armillaria 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 plants in infected areas.
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