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Giant knotweed · Reynoutria sachalinensis

Are there bugs on my giant knotweed?

It is less common for giant knotweed to suffer from severe pest infestations, as it is a very vigorous grower. The most frequent visitors are aphids or spider mites, so check the undersides of the leaves first.

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

Check these first

  1. Look closely at the undersides of the leaves.
  2. Check for sticky residue on the foliage.
  3. Inspect the stems for fine webbing.

Likely causes

  1. Aphids

    Possible

    How to tell: You will see tiny green or black insects clustering on new growth or the undersides of leaves. They often leave behind a sticky residue called honeydew.

    What to do: Wash the leaves gently with a soft cloth and mild soapy water. For larger infestations, use a neem oil spray once a week until they are gone.

  2. Spider Mites

    Possible

    How to tell: Fine webbing appears between the stems or leaves, and the foliage may look speckled or pale. These pests thrive in dry, warm conditions.

    What to do: Increase the humidity around the plant to discourage them. Wipe the leaves down with water or apply insecticidal soap every 5 days for 2 weeks.

Pests on other plants

Find out what's wrong with your giant 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

If the leaves begin to yellow or curl significantly, the infestation is likely heavy. Act quickly to prevent the pests from spreading to other plants.

Stopping it coming back

Regularly inspect your plant and keep it clean by wiping the leaves with a damp cloth.

Giant knotweed: pests? Check yours with a photo

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

Can I use household soap to kill them?
Use a mild, fragrance-free dish soap diluted in water. Avoid harsh detergents that might damage the leaves.
Will these bugs kill my plant?
Giant knotweed is very resilient, but a large infestation can weaken it. Early treatment is always best.

Guides to these causes

More problems with Giant knotweed

Back to the Giant 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.