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

Non-Chemical Management

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.

Select non-chemical management options as your first choice!

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides

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.

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.

Bonide Copper Fungicide Spray or Dust RTU [Organic]
Active ingredient: basic copper sulfate | EPA reg no: 4-58
Monterey Liqui-Cop Copper Fungicidal Garden Spray
Active ingredient: copper-ammonia complex | EPA reg no: 54705-7
Soap-Shield Flowable Liquid Copper Fungicide [Organic]
Active ingredient: copper octanoate | EPA reg no: 67702-2-56872
This list may not include all products registered for this use.

Images

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Caption: Rhododendron fungal leaf spot Photo by: R.S. Byther

WSU Extension

Hortsense