Can I save the leaves that have spots?

It is best to remove them. Once the fungus has established itself, the leaf tissue is usually damaged beyond repair.

Will these spots kill my Musk thistle?

If left untreated, a heavy rust infection can stunt growth and prevent flowering. Early removal of infected parts usually keeps the plant healthy.

Musk thistle: spots, causes and fixes

Check these first

Inspect the undersides of the leaves for orange dust or bumps.
Check if the plant is crowded by other weeds or flowers.
Look for signs of high humidity or poor drainage in the area.

Likely causes

Rust fungus
Most likely
How to tell: You will see small, raised orange or rusty spots on the undersides of the leaves. The leaves may eventually yellow and drop off.
What to do: Remove and destroy all infected leaves immediately to stop the spread. Do not compost these leaves. If the infection is severe, apply a copper based fungicide according to the label instructions.
Poor air circulation
Possible
How to tell: The plant stays damp for too long after rain or dew, creating a perfect home for fungi. This often happens if plants are crowded too close together.
What to do: Thin out nearby vegetation to allow more airflow around your thistle. Ensure your plants have at least 2 to 3 feet of space between them.

Leaf spots on other plants

Find out what's wrong with your musk thistle

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

Worry if the spots cover more than half the leaf surface or start spreading to the stems. A few small spots are manageable, but rapid spread can weaken the plant.

Stopping it coming back

Water at the base of the plant rather than overhead to keep foliage dry. Maintain proper spacing between plants to keep air moving.

Musk thistle: spots? Check yours with a photo

Every plant is a little different. Take a photo of your musk thistle 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

Can I save the leaves that have spots?: It is best to remove them. Once the fungus has established itself, the leaf tissue is usually damaged beyond repair.
Will these spots kill my Musk thistle?: If left untreated, a heavy rust infection can stunt growth and prevent flowering. Early removal of infected parts usually keeps the plant healthy.

Guides to these causes

Rust

Why are there orange spots on my Musk thistle leaves?