Is powdery mildew contagious?

Yes, it spreads through spores in the air. Keep infected plants away from your other greenery.

Should I throw the plant away?

No, it is usually treatable. Just prune the worst parts and improve the environment.

Black horehound: spots, causes and fixes

Check these first

Rub the spot with your finger to see if it wipes off like powder.
Check if the spots are appearing on the top or bottom of the leaves.
Ensure the plant is not crowded by other plants.

Likely causes

Powdery mildew
Most likely
How to tell: It looks like a dusting of white flour on the leaves and stems. The spots will eventually spread to cover the entire leaf surface.
What to do: Remove the most heavily infected leaves immediately to stop the spread. Improve air circulation around the plant and avoid getting water on the leaves when you irrigate.
Water quality issues
Possible
How to tell: Hard water deposits can leave white, crusty spots on the leaves. These spots do not wipe off easily like fungus.
What to do: Wipe the leaves gently with a damp cloth. Use filtered or rainwater for your next few waterings to prevent further buildup.

Leaf spots on other plants

Find out what's wrong with your black horehound

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 serious if it covers the majority of the leaves, as it prevents the plant from photosynthesizing. Small, isolated spots are easy to manage.

Stopping it coming back

Water at the base of the plant rather than overhead, and ensure it has plenty of space for air to move around it.

Black horehound: spots? Check yours with a photo

Every plant is a little different. Take a photo of your black horehound 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 powdery mildew contagious?: Yes, it spreads through spores in the air. Keep infected plants away from your other greenery.
Should I throw the plant away?: No, it is usually treatable. Just prune the worst parts and improve the environment.

Guides to these causes

Powdery Mildew

Why does my Black horehound have white spots?

Check these first

Not sure what's wrong with your black horehound?