Arborvitae: Leaf blight

• Categories: Arborvitae Arborvitae Diseases Conifers Ornamentals
• Last review date: 2026-02-12 10:26

Biology

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

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!

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

Chemical Management

• Make applications in spring and early summer.
• 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.

• 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.