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: Botrytis shoot blight
Photo by: R.S. Byther
  
Rhododendron : Botrytis shoot blight
(revision date: 2/25/2015)


Biology
Botrytis shoot blight is a fungal disease found on shoots in early spring. Symptoms of infection include brown, water-soaked spots on the shoots and masses of gray spores which may be formed on infected tissues. Infected shoots either bend over at the lesion or die back.
Management Options


Non-Chemical Management
  • Good air circulation is essential. Space plantings to allow good air flow and reduce humidity.
  • Avoid overhead watering where possible. If you must use overhead watering, limit to morning hours so foliage will dry during the day.
  • Prune out infected tissue, making cuts into healthy wood and disinfecting pruning tools between cuts.
  • Clean up and destroy any diseased material beneath plants.
Select non-chemical management options as your first choice!

Chemical Management

Apply once in spring when symptoms are first noticed. Homeowners should not make foliar applications to trees over 10 ft tall. Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.

Images

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Caption: Botrytis shoot blight
Photo by: R.S. Byther