Cedar: Leaf blight

categories: Cedar Conifers Ornamentals

revision date: 2023-02-08 12:00

Arborvitae leaves showing light tan areas of leaf blight with darker pitted areas.
Arborvitae Didymascella leaf blight
Photo by: R.S. Byther


Leaf blight is a fungal disease. The symptoms typically appear first in late spring as bleached spots followed by brown or black cushion-like fungal fruiting bodies. Infected foliage may be anywhere on the plant. Individual leaves are killed by the fungus and turn a light tan to gray color. As the fruiting bodies drop out of the leaves, deep pits are left in the dead tissue. The infected tissues often have a “scorched” appearance. Infected leaves often drop in the fall. Western red cedar (Thuja plicata) is most commonly infected, particularly the cultivars ‘Atrovirens’ and ‘Excelsa’. A similar disease attacks junipers.

Management Options

Use Integrated Pest Management (IPM) for successful plant problem management.

Non-chemical Management

Select non-chemical management options as your first choice!

  • Avoid overhead watering. Leaf blight is favored by moist foliage conditions.
  • Plant resistant cultivars.
  • Space plants and prune to allow good air circulation.

Chemical Management

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

  • Apply in spring and early summer.
  • Use Monterey Liqui-Cop Fungicidal Garden Spray on Eastern red cedar only.
  • 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

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

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