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Knotweed · Persicaria

What is eating my knotweed leaves?

If your knotweed leaves look like lace or have large holes, you likely have a visitor. Japanese beetles are the most common culprit during the summer months.

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

Check these first

  1. Look for beetles on the top and bottom of leaves.
  2. Check for slime trails on the soil or stems.
  3. Inspect the plant at night with a flashlight.

Likely causes

  1. Japanese Beetles

    Most likely

    How to tell: You will see metallic green and copper beetles actively feeding on the leaves. They leave behind a skeletonized look where only the veins remain.

    What to do: Pick the beetles off by hand in the early morning when they are sluggish and drop them into a bucket of soapy water. You can also use a fine mesh netting to cover the plant during peak beetle season.

  2. Slugs or Snails

    Possible

    How to tell: These pests leave irregular holes in the leaves and often leave a shiny slime trail behind. They are most active at night.

    What to do: Set out shallow containers of beer or use iron phosphate bait around the base of the plant. Clear away debris or mulch near the stems where they like to hide.

Pests on other plants

Find out what's wrong with your knotweed

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

Take action as soon as you see damage to prevent the plant from losing too much foliage. If the plant is completely skeletonized, it may struggle to recover.

Stopping it coming back

Keep the area around your knotweed clean of debris and monitor for beetles starting in early summer.

Knotweed: pests? Check yours with a photo

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

Are these beetles harmful to me?
No, Japanese beetles are harmless to humans. They are just a nuisance for your garden.
Can I use a pesticide?
Try to avoid sprays as they can harm beneficial insects. Hand picking is the safest and most effective method for small gardens.

Guides to these causes

More problems with Knotweed

Back to the Knotweed 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.