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 lacebug symptoms
Photo by: C.R. Foss
  
Rhododendron : Rhododendron lace bug
(revision date: 3/10/2017)


Biology
The rhododendron lace bug causes stippling on the upper surface of the leaves, and deposits crusty or tar-like excrement on the lower surface. Adult insects are whitish-tan and approximately 1/8" long with lacy-looking wings. Nymphs grow to about 1/8" and are spiny. Infestations are more severe on plants in the sun. Damage is usually apparent by early to mid-July. While almost never fatal, repeated infestations of rhododendron lace bugs may result in yellowed, sickly plants. This insect is not found on azaleas. Rhododendron lace bug has one generation per year. It overwinters as eggs laid on the underside of leaves, usually along leaf veins. See also Azalea: Azalea lace bug.
Management Options


Non-Chemical Management
  • Some spiders and insects such as assassin bugs and minute pirate bugs may help control the population naturally.
  • Hand removal of adults and nymphs on a regular basis will limit the amount of visible damage.
Select non-chemical management options as your first choice!

Chemical Management

Apply in spring when nymphs appear. Difficult to control with one application. Avoid using Sevin (carbaryl) if there is any possibility of pesticide drifting onto nearby blooming plants. These products are toxic to bees. 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
  • GardenTech Sevin Conc Bug Killer
    Active ingredient: carbaryl  |  EPA reg no: 264-334-71004
  • 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
  • This list may not include all products registered for this use.
Images

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Caption: Rhododendron lacebug symptoms
Photo by: C.R. Foss
Caption: Rhododendron lacebug symptoms
Photo by: C.R. Foss
Caption: Rhododendron lacebug
Photo by: A.L. Antonelli