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Northern white cedar · Thuja occidentalis

Why are there strange bags on my Northern white cedar?

Seeing odd, silk-covered structures hanging from your cedar is a sign of bagworms. These caterpillars can quickly strip your tree of its foliage if left unchecked. Check your branches closely for these camouflaged pests.

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pests on a plant
Photo: Jules Verne Times Two, CC BY-SA 4.0

Check these first

  1. Inspect the branches for small, hanging silk bags.
  2. Look for fine webbing between the needles.
  3. Check if the foliage color is fading to a dull bronze.

Likely causes

  1. Bagworm infestation

    Most likely

    How to tell: You will see small, cone-shaped bags made of silk and bits of cedar foliage hanging from the twigs. The tree may show patches of missing needles where the larvae have been feeding.

    What to do: Pick the bags off by hand and drop them into a bucket of soapy water. If the infestation is heavy, apply a biological insecticide like Bacillus thuringiensis in early summer when the larvae are small.

  2. Spider mites

    Possible

    How to tell: The foliage takes on a dusty, yellow or bronze appearance during hot, dry weather. You might see fine webbing between the needles if you look very closely.

    What to do: Spray the foliage down with a strong stream of water early in the morning to dislodge the mites. If they persist, use an insecticidal soap or neem oil spray once a week for 3 weeks.

Pests on other plants

Find out what's wrong with your northern white cedar

The list above covers the usual causes. Pocket Botanist looks at a photo of your actual plant and tells you the likely cause, how serious it is, and what to try first. Identification and a health check are free.

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When to worry

If you see large numbers of bags or if the tree is losing significant amounts of foliage, take action immediately. A few bags can be managed easily, but a full infestation can kill the tree.

Stopping it coming back

Monitor your tree regularly starting in late spring. Keep the tree healthy with proper watering, as stressed trees are more attractive to pests.

Northern white cedar: pests? Check yours with a photo

Every plant is a little different. Take a photo of your northern white cedar and Pocket Botanist tells you which cause is most likely, how serious it is, and what to try first. A few checks a day are free. Save the plant and you get care reminders timed for it.

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Questions people ask

Can I just leave the bags on the tree?
No, you should remove them. The bags contain eggs that will hatch into more caterpillars next season, leading to a much larger problem.
Are spider mites harmful?
Yes, they suck the sap from the needles, which weakens the tree and causes the foliage to discolor. They thrive in hot, dry conditions.

Guides to these causes

More problems with Northern white cedar

Back to the Northern white cedar guide

This article was generated with AI on from the plant’s care profile and is general information, not horticultural advice. Read about how we build these guides.