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 whitefly
Photo by: A.L. Antonelli
  
Rhododendron : Rhododendron whitefly
(revision date: 3/8/2016)


Biology
Whiteflies are small white insects that hold their wings rooflike over their abdomens rather than flat like true flies. Infested leaves, usually the tender young leaves at the branch tips, are mottled yellow on the upper surface, and the margins often curl. Rhododendron whiteflies often leave white powdery residues on the leaf surface. Rhododendrons with smooth surfaces underneath the leaf are most affected. Whiteflies can produce large amounts of sticky honeydew, which can develop a heavy coating of black sooty mold. The rhododendron whitefly is mainly an aesthetic pest, although heavy infestations can damage susceptible plants.
Management Options


Non-Chemical Management
  • Do not overfertilize. Whitefly numbers increase with increasing foliar nitrogen levels. If necessary, switch to a slow-release fertilizer and/or one with less nitrogen.
  • Lightly vacuum plants in the early morning to remove cold, slow-moving whiteflies.
Select non-chemical management options as your first choice!

Chemical Management

Several applications may be necessary about 7 days apart. Apply when 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.

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
  • This list may not include all products registered for this use.
Images

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Caption: Rhododendron whitefly
Photo by: A.L. Antonelli