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Oak · Quercus

What are these growths on my oak tree's leaves?

Those strange bumps or growths are likely caused by gall wasps. While they look alarming, they rarely cause any real harm to the health of your oak.

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

Check these first

  1. Examine the growths to see if they are hard or soft.
  2. Check the undersides of leaves for small insects.
  3. Look for sticky residue on the leaves or ground.

Likely causes

  1. Gall Wasps

    Most likely

    How to tell: You will see abnormal, round, or spiky growths on leaves, twigs, or buds. These are created by the tree in response to wasp larvae.

    What to do: No treatment is necessary as these do not damage the tree. Simply prune away any affected branches if you find them unsightly.

  2. Scale Insects

    Possible

    How to tell: Small, bump like insects appear on twigs or leaves, often accompanied by sticky honeydew. They suck sap and can weaken the tree if the infestation is heavy.

    What to do: Apply horticultural oil during the dormant season to smother the insects. For active infestations, use a systemic insecticide recommended by a professional.

Pests on other plants

Find out what's wrong with your oak

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

Galls are almost never a reason to worry. You should only be concerned if scale insects are causing significant branch dieback or heavy leaf drop.

Stopping it coming back

Keep your oak healthy with proper watering and care to help it resist minor pest issues.

Oak: pests? Check yours with a photo

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

Do I need to spray my tree for galls?
No, spraying is ineffective and unnecessary. The galls are just a cosmetic issue.
Will the wasps hurt me?
No, these tiny wasps are focused on the tree and are not aggressive toward humans.

Guides to these causes

More problems with Oak

Back to the Oak 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.