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: Rhododendron physiological leaf spot
Photo by: R.S. Byther
  
Rhododendron : Physiological leaf spot
(revision date: 4/23/2014)


Biology
Rhododendron leaves sometimes develop variously-sized and -shaped spots. These are usually dark purple in color. The exact cause is unknown, but cultural or environmental stress may result in physiological leaf spot. One particularly susceptible variety is the rhododendron Mrs. G.W. Leak. This problem does not usually cause any permanent harm to the plant.
Management Options


Non-Chemical Management
  • Provide proper culture for the plants, especially proper watering and fertilization.
  • Plant less-susceptible varieties in highly visible locations where physiological leaf spot would be an aesthetic problem.
Select non-chemical management options as your first choice!

Chemical Management

None recommended

Images

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Caption: Rhododendron physiological leaf spot
Photo by: R.S. Byther