Is this fungus harmful to me?

No, powdery mildew is specific to plants and will not harm humans or pets. Just wash your hands after handling infected leaves.

Should I throw away the infected leaves?

Yes, do not compost them. Put them in the trash to prevent the fungal spores from spreading further in your garden.

Perennial sowthistle: spots, causes and fixes

Check these first

Rub the white spots to see if they wipe off like dust.
Check if the plant is crowded by other garden weeds or flowers.
Observe if the spots appear after a period of high humidity.

Likely causes

Powdery mildew
Most likely
How to tell: Leaves develop a white, floury appearance that can eventually cover the entire surface. It often starts on older leaves near the base.
What to do: Remove and discard the most heavily infected leaves. Spray the remaining foliage with a mixture of 1 tablespoon of baking soda in 1 gallon of water.
Poor air circulation
Possible
How to tell: The plant is crowded by other vegetation, preventing leaves from drying out. This creates the perfect environment for fungal spores to grow.
What to do: Thin out nearby plants to improve airflow. Make sure your sowthistle has enough space to breathe.

Leaf spots on other plants

Find out what's wrong with your perennial 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

Powdery mildew is rarely fatal but it makes the plant look unsightly and reduces its vigor. Treat it early to prevent it from spreading to your other garden plants.

Stopping it coming back

Water at the base of the plant rather than overhead to keep the foliage dry. Ensure your sowthistle is planted in a sunny, open location.

Perennial sowthistle: spots? Check yours with a photo

Every plant is a little different. Take a photo of your perennial sowthistle 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

Is this fungus harmful to me?: No, powdery mildew is specific to plants and will not harm humans or pets. Just wash your hands after handling infected leaves.
Should I throw away the infected leaves?: Yes, do not compost them. Put them in the trash to prevent the fungal spores from spreading further in your garden.

Guides to these causes

Powdery Mildew

Why does my perennial sowthistle have white spots?