Cedar: Leaf blight

categories: Cedar Conifers Ornamentals

last review date: 2026-03-21 04:59

Biology

Leaf blightis 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

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. 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

Examples of pesticides that are legal for home use in Washington State are listed below.
The list may not include all products registered for this use.

• Monterey Liqui-Cop Copper Fungicidal Garden Spray
  Active ingredient: copper-ammonia complex (EPA reg. 54705-7)