Troubleshooting
Western Red Cedar problems — and how to fix them
Western Red Cedar (Thuja plicata) is generally forgiving once you match its basics, but a few issues come up again and again. Here is what each one looks like, why it happens, and the fix.
Didymascella Leaf Blight
A fungal disease causing browning of inner scale leaves and dieback, especially in dense hedging or high-humidity sites with poor air circulation. Improve spacing and prune to open the canopy. Copper-based fungicide sprays in early spring provide protective control.
Bagworm (Thyridopteryx ephemeraeformis)
Caterpillars construct silk-and-foliage bags, feeding on and defoliating branches. Hand-pick bags from small trees in winter when bags are visible. Btk spray applied at caterpillar hatch in late spring is effective on young larvae.
Windburn and Winter Desiccation
Exposed plants in zones 5–6 can suffer browning of foliage from cold, dry winter winds drawing moisture from foliage faster than frozen roots can replace it. Apply anti-desiccant spray in late autumn; shelter young trees with burlap windbreaks in their first 2 winters.
Prevent western red cedar problems before they start
Most western red cedar issues are care-mismatch, not bad luck. Dial in the basics:
Looking for western red cedar in general rather than its problems? Read the full western red cedar care guide — light, water, soil and feeding.
Western Red Cedar problems — FAQ
Why is my western red cedar didymascella leaf blight?
A fungal disease causing browning of inner scale leaves and dieback, especially in dense hedging or high-humidity sites with poor air circulation. Improve spacing and prune to open the canopy. Copper-based fungicide sprays in early spring provide protective control.
Why is my western red cedar bagworm (thyridopteryx ephemeraeformis)?
Caterpillars construct silk-and-foliage bags, feeding on and defoliating branches. Hand-pick bags from small trees in winter when bags are visible. Btk spray applied at caterpillar hatch in late spring is effective on young larvae.
Why is my western red cedar windburn and winter desiccation?
Exposed plants in zones 5–6 can suffer browning of foliage from cold, dry winter winds drawing moisture from foliage faster than frozen roots can replace it. Apply anti-desiccant spray in late autumn; shelter young trees with burlap windbreaks in their first 2 winters.