Leaf Blight (Keithia Blight)
Didymascella thujina
3 host plants
Last updated
This profile synthesizes data from multiple published sources. Expert field review is in progress.
Western red cedar develops small bleached spots on young leaves, turning brown with apothecia visible; leaves drop by fall. Didymascella thujina requires wet conditions during summer spore discharge. Plant resistant cultivars (Atrovirens and Excelsa are susceptible), space for air drying, and avoid downwind planting near infected hedges.
Remove blighted tissue promptly, cutting well below visible symptoms. Improve air circulation by thinning dense growth. Avoid overhead watering, especially during bloom and new growth periods when tissues are most susceptible. For recurring problems, preventive fungicide applications timed to protect new growth can reduce infection, but cultural controls should be your first approach.
Quick Reference
Management
Spring (bud break through summer). New foliage most susceptible.
Spring spore release from pseudothecia; wet conditions during new needle elongation.
Cultural Controls
- Propagate from disease-free stock plants.
- Use seed from British Columbia coastal, low-elevation populations.
- Space nursery plants and time irrigation to promote rapid drying of foliage.
- Do not grow susceptible cultivars downwind of infected hedges, windbreaks, or nearby stands of native western red cedar.
- Pruning out and burning affected twigs is of limited use.
- Remove plant debris from seed before seeding.