Should I cut off all the spotted leaves?

Yes, removing them helps prevent the fungus from jumping to healthy parts of the plant. Just make sure to use clean scissors.

Will these spots kill my plant?

Usually not, unless the infection is severe and covers most of the foliage. Keep the plant healthy and it should recover.

spiny sowthistle: spots, causes and fixes

Check these first

Inspect the undersides of leaves for tiny insects.
Check if the leaves are staying wet after watering.
Look for signs of white or gray fuzz.

Likely causes

Fungal Leaf Spot
Possible
How to tell: You will see small brown or black circles often with a yellow halo around them. These spots tend to spread when the foliage stays wet for too long.
What to do: Remove the affected leaves immediately to stop the spread. Improve airflow around the plant and avoid overhead watering to keep the foliage dry.
Downy Mildew
Possible
How to tell: This shows up as yellow patches on the top of the leaf with fuzzy gray growth underneath. It thrives in cool and damp conditions.
What to do: Increase the space between your plants to allow better air circulation. Apply a copper based fungicide if the infection continues to spread.

Find out what's wrong with your spiny sowthistle

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 are spreading rapidly across the entire plant. A few small spots on older lower leaves are usually just part of the natural aging process.

Stopping it coming back

Water only at the base of the plant and ensure it gets plenty of direct sunlight to dry off quickly.

Keep your spiny sowthistle healthy from here

Save your plant in Pocket Botanist and you get care reminders timed for this plant, plus a care history that shows what worked. Identification and a health check are free.

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Questions people ask

Should I cut off all the spotted leaves?: Yes, removing them helps prevent the fungus from jumping to healthy parts of the plant. Just make sure to use clean scissors.
Will these spots kill my plant?: Usually not, unless the infection is severe and covers most of the foliage. Keep the plant healthy and it should recover.

Why does my spiny sowthistle have spots on its leaves?