WSU Extension


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) 
Salt injury 
Tissue proliferation 
Azalea bark scale 
Lecanium scale 
Rhododendron lace bug 
Rhododendron whitefly 
Root weevils 

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Caption: Aphid damage on rhododendron
Photo by: A.L. Antonelli
Rhododendron : Aphids
(revision date: 3/22/2021)

Aphids cause twisting, curling, or puckering of new growth by their feeding. Whitish cast skins and green live aphids may be visible on the undersides of leaves. Honeydew, a shiny, sticky substance excreted by aphids, may be present on the leaves, as may sooty mold, a black fungus which grows on the honeydew.
Management Options

Non-Chemical Management
  • Natural aphid predators such as ladybird beetles, lacewings, parasitic wasps, and syrphid or hover flies can maintain aphid populations at reasonable levels.
  • Aphids can be washed from foliage with a strong stream of water.
  • Maintain proper plant nutrition. Healthy plants are less susceptible to insect damage, and high nitrogen levels in the foliage encourages aphid reproduction.
Select non-chemical management options as your first choice!

Chemical Management

Thorough coverage of the foliage including lower leaf surfaces is important when using foliar sprays. Follow label instructions for products applied as a drench. Apply one of the following when aphids are 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.

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.
  • Safer Brand BioNEEM Multi-Purpose Insecticide & Repellent Conc [Organic]
    Active ingredient: azadirachtin  |  EPA reg no: 70051-6-42697
  • Safer Brand Garden Defense Multi-Purpose Spray Conc [Organic]
    Active ingredient: clarified hydrophobic extract of neem oil  |  EPA reg no: 70051-2-42697
  • Safer Brand Insect Killing Soap Conc II [Organic]
    Active ingredient: potassium salts of fatty acid  |  EPA reg no: 42697-60
  • This list may not include all products registered for this use.

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Caption: Aphid damage on rhododendron
Photo by: A.L. Antonelli
Caption: Aphid colony
Photo by: Unknown
Caption: Aphid cast skins
Photo by: R.S. Byther