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Cedar Leaf Blight

Disease

Cedar Leaf Blight is a fungal disease that targets the foliage of Western Red Cedars. It matters because it causes premature needle drop and can significantly thin the canopy of affected trees.

Cedar Leaf Blight on a plant
Photo: Chris Fluit, CC BY

Symptoms by part

Leaves

Small brown spots appear on the needles, which eventually turn gray or tan and drop off prematurely.

Causes

  • Prolonged periods of wet, humid weather
  • Poor air circulation within the tree canopy
  • High density planting that traps moisture

Could be confused with

  • Drought stress · Drought causes needles to turn brown uniformly across the tree rather than showing distinct spots.
  • Winter burn · Winter burn typically affects the outer, exposed needles after cold, windy weather rather than appearing as discrete spots.

Treatment

  1. Prune away and destroy heavily infected branches to improve airflow through the center of the tree.
  2. Clear away all fallen needles and debris from beneath the tree to remove fungal spores.
  3. Thin out dense branches to allow sunlight and air to reach the inner foliage.

Without chemicals

  • Pruning to increase canopy ventilation
  • Sanitation by removing and disposing of infected fallen needles
  • Spacing new plantings further apart to reduce humidity

Preventing it

  • Choose planting sites with excellent drainage and good sun exposure.
  • Space trees appropriately to ensure they have room to grow without touching.
  • Avoid overhead watering that keeps the foliage wet for long periods.

Season

The warm growing season, especially during wet spells.

Spread risk

Moderate

Severity

Moderate

When to act

Act as soon as you notice significant needle drop or spotting during the growing season. If the tree loses more than half of its foliage or shows signs of structural decline, consult a tree surgeon for an assessment.

Think it's Cedar Leaf Blight?

This guide covers the general picture. Pocket Botanist looks at your actual plant from a photo and tells you what's really going on, how serious it is, and what to try first. Identification and a health check are free.

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Questions people ask

Will my tree die from Cedar Leaf Blight?
Usually not, but it can weaken the tree and make it look thin and unhealthy over several years.
Can I stop the spread by watering less?
Reducing overhead watering helps, but you cannot control rainfall, so focus on pruning to improve airflow instead.

Plants it affects

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This guide was generated with AI and is general information, not horticultural advice. Read about how we build these guides.