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Arborvitae · Thuja

Why are there strange bags on my Arborvitae?

Seeing odd, cone shaped structures hanging from your branches usually means you have bagworms. These caterpillars can strip a tree bare if left alone, so check your foliage closely for these camouflaged nests.

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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 hanging silk bags.
  2. Look for fine webbing near the base of the needles.
  3. Check if the foliage color is fading or turning bronze.

Likely causes

  1. Bagworms

    Most likely

    How to tell: You will see small, spindle shaped bags made of silk and bits of leaves hanging from the twigs.

    What to do: Pick the bags off by hand and drop them into a bucket of soapy water. If the infestation is heavy, spray the foliage with a product containing Bacillus thuringiensis in early summer when the young larvae are active.

  2. Spider Mites

    Possible

    How to tell: The foliage looks dusty or bronzed, and you might see fine webbing between the needles.

    What to do: Spray the tree with a strong stream of water to knock the mites off. If they persist, apply horticultural oil or insecticidal soap according to the label directions.

Pests on other plants

Find out what's wrong with your arborvitae

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

You should worry if you see more than a few bags, as they can quickly spread and defoliate the entire plant. A few isolated bags are easy to manage if caught early.

Stopping it coming back

Keep your tree healthy with regular deep watering and monitor it closely during the spring and summer months.

Arborvitae: pests? Check yours with a photo

Every plant is a little different. Take a photo of your arborvitae 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

Will bagworms kill my tree?
Yes, if the infestation is severe enough to strip most of the foliage, the tree will struggle to survive. Early removal is the best way to save the plant.
Can I just pull the bags off?
Yes, hand picking is the most effective way to control them on smaller trees. Make sure to dispose of them in soapy water so the larvae do not crawl back out.

Guides to these causes

More problems with Arborvitae

Back to the Arborvitae 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.