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 



print version| pdf version| email url    
Caption: Azalea bark scale and sooty mold
Photo by: A.L. Antonelli
  
Rhododendron : Azalea bark scale
(revision date: 3/10/2017)


Biology
The azalea bark scale is a soft scale resembling mealybugs. Red females cover themselves and their eggs with a white, waxy protective coating. Cottony masses of the scales are often located on twigs and in the forks of the branches. Sticky honeydew is excreted by the pests, and may have black sooty mold growing on it.
Management Options


Non-Chemical Management
  • Keep plants healthy. Vigorous plants are more able to tolerate scale damage.
  • Several species of ladybird beetles and parasitic wasps help control scale populations. Avoid use of broad-spectrum insecticides which can kill these predators.
  • Prune and destroy leaves or stems that are severely affected to help control minor infestations.
  • Hand-picking to remove insects may control small infestations.
  • Provide proper plant nutrition. Like aphids, scale populations increase with high plant nitrogen levels. If necessary, change to a slow-release fertilizer or one with less nitrogen.
Select non-chemical management options as your first choice!

Chemical Management

Scout for crawlers. Apply to control the immature crawler stage, usually in late spring to early summer. 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.
  • Bayer Advanced Power Force Multi-Insect Killer R-T-S
    Active ingredient: cyfluthrin  |  EPA reg no: 72155-39
  • Bonide Systemic Insect Control
    Active ingredient: acephate  |  EPA reg no: 239-2461-4
  • 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 laurate  |  EPA reg no: 42697-60
  • This list may not include all products registered for this use.
Images

+ Show larger images

 
Caption: Azalea bark scale and sooty mold
Photo by: A.L. Antonelli