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 Phytophthora blight
Photo by: J.W. Pscheidt
  
Rhododendron : Phytophthora blight
(revision date: 4/23/2014)


Biology
Phytophthora blight is a fungal disease whose symptoms are often confused with chemical or mechanical injury or leaf scorch. Irregular dead spots on the tips or margins of leaves, shiny black cankers on shoots, and leaf loss and tip dieback on affected branches are among the common symptoms. Several species of Phytophthora fungi can cause these symptoms. This disease is spread by wind and splashing water, but does not typically spread to neighboring, unrelated plant species. Do not confuse Phytophthora blight with Ramorum leaf and shoot blight, also caused by a Phytophthora species. See Rhododendron: Ramorum leaf and shoot blight for additional information.
Management Options


Non-Chemical Management
  • Avoid wounding plants, as wounds provide ideal infection sites.
  • Remove infected leaves. Prune infected branches back into healthy wood. Destroy, do not compost, diseased plant material.
  • Rake and destroy fallen leaves to prevent the spread of infection.
  • Avoid overhead watering.
Select non-chemical management options as your first choice!

Chemical Management

Phytophthora blight is generally not a problem in the landscape. If it should develop as a problem, use sanitation and other cultural methods to manage the problem.

Images

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Caption: Rhododendron Phytophthora blight
Photo by: J.W. Pscheidt