Rhododendron: Leaf spot

• Categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs
• Last review date: 2025-06-27 11:14

Biology

Several fungi cause leaf spots on rhododendron. They often infect through wounds.

Infected leaves display dark brown spots which may cover up to half of the leaf surface. These spots may feel bumpy on the surface due to the presence of fungal structures.

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!

• Avoid overhead watering and maintain good air circulation in plantings.
• Prevent injury to reduce likelihood of infection.
• Provide proper culture for plants.
• Prune out and destroy all infected tissues.
• Clean up and destroy any fallen leaves to prevent spread of infection.

Chemical Management

• Read label for application timing.
• 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.

• Bonide Copper Fungicide Spray or Dust RTU [Organic]
  Active ingredient: basic copper sulfate
  EPA registration number: 4-58
• Monterey Liqui-Cop Copper Fungicidal Garden Spray
  Active ingredient: copper-ammonia complex
  EPA registration number: 54705-7
• Soap-Shield Flowable Liquid Copper Fungicide [Organic]
  Active ingredient: copper octanoate
  EPA registration number: 67702-2-56872
• This list may not include all products registered for this use.