WSU Extension

Hortsense

Caption: Phytophthora root rot symptoms
Photo by: R.S. Byther
  
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True Fir : Phytophthora root rot
(revision date: 4/23/2014)


Biology
Phytophthora root rot is usually a problem only in areas with poor drainage or where flooding occurs. The fungus attacks the roots, which rot and die. The infection moves up into the crown, where the cambium (soft inner bark) turns reddish-brown or caramel in color instead of the normal white to greenish color. Older trees may develop cankers on the trunk, which are a dark reddish-brown when cut. The cankers may be accompanied by split bark and oozing pitch. Lower branches wilt, turn dark red, and die back. Younger trees are often killed outright, while infected mature trees may show wilting, branch dieback, and/or gradual decline.
Management Options

Non-Chemical Management
  • Prevent disease by planting only disease-free materials.
  • Do not plant in waterlogged, poorly drained, or frequently flooded areas.
  • Improve soil drainage by incorporating organic material or using raised beds.
  • Avoid soil compaction, which reduces drainage. Construction, heavy foot traffic, or machinery can compact soil.
  • Remove and destroy all infected plants and plant debris.
  • Plant resistant species in infected areas. Your county Extension agent or WSU Master Gardeners can make recommendations.
Select non-chemical management options as your first choice!

Chemical Management


None recommended

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Caption: Phytophthora root rot symptoms
Photo by: R.S. Byther
Caption: Phytophthora root rot causing cinnamon-brown discoloration
Photo by: R.S. Byther
Caption: Phytophthora root rot symptoms
Photo by: C.R. Foss