Will the white spots kill my plant?

Usually not, but it can make the plant look messy and reduce its vigor. Treating it early keeps the plant healthy.

Can I use a fungicide?

Yes, you can use a garden-safe neem oil or a copper fungicide if the baking soda mix does not work. Follow the label instructions carefully.

Prostrate knotweed: spots, causes and fixes

Check these first

Rub the white spots with your finger to see if they wipe off like dust.
Look at the spacing between your plants to see if they are crowded.
Check if the spots are located on the leaves getting the most direct sun.

Likely causes

Powdery Mildew
Most likely
How to tell: You will see a white, floury coating on the surface of the leaves. It often starts as small spots and spreads to cover the entire foliage.
What to do: Prune away the most heavily infected stems to improve circulation. Spray the remaining foliage with a mixture of one tablespoon of baking soda in a gallon of water. Apply this once a week until the white growth disappears.
Sunburn
Possible
How to tell: The spots appear as bleached, tan, or white patches on leaves that receive the most intense afternoon sun. These spots are dry and brittle rather than dusty.
What to do: Provide a light shade cloth during the hottest part of the day if the heat is extreme. Ensure the plant is well hydrated so it can handle the intense sun better.

Leaf spots 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.

When to worry

If the mildew covers more than half of the plant, it can weaken the stems significantly. A few small spots are common during humid spells and are usually easy to manage.

Stopping it coming back

Space your plants out to allow air to move freely between them. Water at the base of the plant rather than overhead to keep the leaves dry.

Prostrate knotweed: spots? 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.

Get the app · Or check it from a photo now, free

Questions people ask

Will the white spots kill my plant?: Usually not, but it can make the plant look messy and reduce its vigor. Treating it early keeps the plant healthy.
Can I use a fungicide?: Yes, you can use a garden-safe neem oil or a copper fungicide if the baking soda mix does not work. Follow the label instructions carefully.

Guides to these causes

Powdery Mildew

Why does my prostrate knotweed have white spots?

Check these first

Not sure what's wrong with your prostrate knotweed?