WSU Extension


Cedar flagging 
Leaf blight 
Port Orford cedar root rot 
Seiridium canker 

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Caption: Seiridium canker
Photo by: M. Harris
Cedar : Seiridium canker
(revision date: 3/17/2021)

Seiridium cardinale and Phaeobotryon cupressi are fungal pathogens which cause yellowing or browning of the foliage. The result is flagging, the dieback of branch tips and entire branches of trees in a random distribution throughout the canopy. Cankers may be observed which are wounds or necrotic lesions often sunken beneath the surface of the stems or branches. Fungal spores can be spread by rain, irrigation water, insects, or pruning tools. The spores can enter through wounds or cracks in the bark, insect holes, or storm damage. Environmental factors such as drought or storm damage may cause stress on trees which make them vulnerable to these fungi. In the Pacific Northwest Incense cedar is particularly susceptible to this disease. Other possible hosts might include Leyland cypress, False cypress, Monterey cypress, Arborvitae, and Junpier.
Management Options

Non-Chemical Management
  • Give the plants appropriate care. This keeps trees vigorous and helps them to better resist disease.
  • Provide sufficient water especially during drought conditions. To retain moisture apply mulch a few inches away from the trunk.
  • To manage the disease, make pruning cuts well below the infected area during dry weather and especially before fall rains. Sterilize pruning tools between each cut to avoid spreading disease. Remove and destroy infected branches.
  • Plant disease resistant varieties such as western red cedar.
Select non-chemical management options as your first choice!

Chemical Management

None recommended.


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Caption: Seiridium canker
Photo by: M. Harris
Caption: Seiridium canker branch dieback
Photo by: M. Harris
Caption: Seiridium canker flagging symptoms
Photo by: M. Harris
Caption: Seiridium canker random flagging
Photo by: M. Harris