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: Looper on rhododendron
Photo by: S.J. Collman
Rhododendron : Caterpillars
(revision date: 4/24/2015)

Several caterpillar pests occur on rhododendrons, most notably cutworms, loopers, and the obliquebanded leafroller. Cutworms and loopers (various species) feed on leaf tissue, removing large, irregularly-shaped pieces. They are night-feeders and may not be seen on the leaves in the daytime. Obliquebanded leafrollers are usually found on the new growth. Their presence can be determined by the presence of rolled leaves held in place with webbing. The feeding caterpillar can be found inside the rolled leaf.
Management Options

Non-Chemical Management
  • Naturally-occurring predators such as birds and predaceous ground beetles will help control caterpillar pests, as will parasitic insects.
  • Hand removal of the night-feeding caterpillars can help control their numbers, while the leafrollers can be pinched in the rolled leaves to kill them.
Select non-chemical management options as your first choice!

Chemical Management

Apply when caterpillars are first noticed. Bacillus thuringiensis (Bt) will control leafrollers only if they are actively feeding. Use a spreader-sticker with liquid Bt formulations. 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.
  • ferti-lome Dipel Dust
    Active ingredient: Bacillus thuringiensis subsp. kurstaki  |  EPA reg no: 7401-290
  • Safer Brand BioNEEM Multi-Purpose Insecticide & Repellent Conc [Organic]
    Active ingredient: azadirachtin  |  EPA reg no: 70051-6-42697
  • Safer Brand Caterpillar Killer for Trees, Shrubs & Vegetables Conc II [Organic]
    Active ingredient: Bacillus thuringiensis subsp. kurstaki  |  EPA reg no: 70051-106-42697
  • Safer Brand Caterpillar Killer/Trees, Shrubs, & Vegetables Conc
    Active ingredient: Bacillus thuringiensis subsp. kurstaki  |  EPA reg no: 42697-23
  • This list may not include all products registered for this use.

+ Show larger images

Caption: Looper on rhododendron
Photo by: S.J. Collman
Caption: Cutworm damage on rhododendron
Photo by: A.L. Antonelli
Caption: Cutworm eggs
Photo by: A.L. Antonelli
Caption: Celery looper pupa
Photo by: A.L. Antonelli