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prostrate knotweed · Polygonum aviculare

What are these pests on my prostrate knotweed?

It is less common for prostrate knotweed to get pests, but they can appear if the plant is stressed. The most common issue is powdery mildew, which looks like a white dusting on the leaves.

Not sure it's this? Check a photo of your plant for free

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

Check these first

  1. Check the undersides of leaves for tiny bugs.
  2. Look for white powdery spots on the foliage.
  3. Inspect the stems for sticky residue.

Likely causes

  1. Powdery mildew

    Possible

    How to tell: You will see a white, floury coating on the surface of the leaves. It usually happens when there is poor air circulation around the plant.

    What to do: Move the plant to a spot with better airflow and wipe the leaves with a damp cloth. If it persists, use a neem oil spray once a week until the white spots disappear.

  2. Aphids

    Possible

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

    What to do: Wash the plant off with a gentle stream of water in the sink. If they remain, apply insecticidal soap once every 5 days for two weeks.

Pests on other plants

Find out what's wrong with your prostrate 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

Worry if you see the plant's growth slowing down or leaves curling due to heavy infestation. It is normal to see the occasional stray bug, but an active colony needs treatment.

Stopping it coming back

Ensure your plant has plenty of space and good air circulation to prevent fungal issues like mildew.

Prostrate knotweed: pests? Check yours with a photo

Every plant is a little different. Take a photo of your prostrate 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 dish soap to kill bugs?
A very mild solution of water and a drop of plain dish soap can work, but insecticidal soap is safer for the plant. Avoid using soaps with heavy fragrances or degreasers.
Is powdery mildew contagious?
Yes, it can spread to other plants nearby through air currents. Isolate your knotweed until the white growth is completely gone.

Guides to these causes

More problems with prostrate knotweed

Back to the prostrate 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.