Rhododendron: Caterpillars

• Categories: Ornamentals Rhododendron Rhododendron Insects Shrubs
• Last review date: 2025-06-27 09:57

Biology

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

See "Using Integrated Pest Management (IPM) in the Landscape" for successful problem management techniques.

Non-chemical Management

Select non-chemical management options as your first choice!

• 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.

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.

Approved Pesticides

If you choose to use a pesticide, some examples of products that are legal in Washington are listed below. Some products are labeled for just INDOOR or just OUTDOOR use, or may allow both uses. Be sure to choose a product appropriate for your situation. Always read and follow all label directions.

• ferti-lome Dipel Dust
  Active ingredient: Bacillus thuringiensis subsp. kurstaki
  EPA registration number: 7401-290
• Safer Brand BioNEEM Multi-Purpose Insecticide and Repellent Concentrate [Organic]
  Active ingredient: azadirachtin
  EPA registration number: 70051-6-42697
• Safer Brand Caterpillar Killer for Trees, Shrubs and Vegetables Concentrate II [Organic]
  Active ingredient: Bacillus thuringiensis subsp. kurstaki
  EPA registration number: 70051-106-42697
• This list may not include all products registered for this use.