WSU Extension

Hortsense

Rhododendron
 
Disease
Armillaria root rot 
Botrytis shoot blight 
Gray blight 
Leaf spot 
Lime-induced chlorosis 
Marginal leaf necrosis 
Physiological leaf spot 
Phytophthora blight 
Phytophthora root rot 
Powdery mildew 
Ramorum leaf and shoot blight (Sudden oak death) 
Rust 
Salt injury 
Sunburn 
Tissue proliferation 
Insect
Aphids 
Azalea bark scale 
Caterpillars 
Lecanium scale 
Rhododendron lace bug 
Rhododendron whitefly 
Root weevils 



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Caption: Phytophthora root rot on rhododendron
Photo by: R.S. Byther
  
Rhododendron : Phytophthora root rot
(revision date: 4/23/2014)


Biology
The symptoms produced by Phytophthora root rot are often confused with those caused by environmental or cultural problems. Above ground, infected plants may show stunting, yellowish-green leaves, branch dieback, wilt, and even plant death. Dead leaves persist on the branches instead of dropping. Underground, the roots rot, progressing from the smallest to the largest. The fungus may also cause rot in the main stem. Phytophthora persists in the soil and can infect new plants. Diseased plant tissues and debris are other sources of infection.
Management Options


Non-Chemical Management
  • Select resistant rhododendron species such as Rhododendron davidsonianum 'Serenade', R. delavayi, R. glomerulatum, R. hyperethrum, R. lapponicum, R. occidentale, R. pseudochrysanthum, R. quinquefolium, R. sanctum, R. simsii, R. websterianum. Resistant varieties include 'Caroline', 'Martha Isaacson', 'Pink Trumpet', 'Professor Hugo De Vries', 'Red Head'.
  • Choose the right plant for your location. A healthy plant is more resistant to disease.
  • Prevent disease by planting only disease-free materials.
  • Practice good sanitation to prevent the spread of disease.
  • Remove and destroy all infected plants.
Select non-chemical management options as your first choice!

Chemical Management

None recommended

Images

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Caption: Phytophthora root rot on rhododendron
Photo by: R.S. Byther