Pocket Botanist
Check these first
- Look closely for a white powdery residue.
- Check if the spots are soft or dry.
- Ensure the plant has enough space for airflow.
Likely causes
Powdery mildew
Most likelyHow to tell: You will see a white or gray powdery substance on the leaf surfaces. It often spreads quickly in humid, stagnant air.
What to do: Wipe the leaves with a damp cloth and improve air circulation around the plant. Use a neem oil spray if the infection persists.
Fungal leaf spot
PossibleHow to tell: Small brown or black spots appear on the leaves, sometimes with a yellow halo. These spots often grow larger over time.
What to do: Remove the affected leaves immediately to stop the spread. Avoid getting water on the foliage when you water the soil.
When to worry
Small, isolated spots are manageable, but if they cover more than half the leaf surface, the plant is struggling. Act quickly to prevent the fungus from spreading to the stems.
Stopping it coming back
Water at the base of the plant to keep leaves dry and ensure the plant is not crowded by other foliage.
Not sure which one it is? Photograph your common hogweed.
This page lists the usual causes. Pocket Botanist looks at your actual leaf and tells you the likely cause, how serious it is, and what to try first. Identification and a health check are free.
Questions people ask
- Is powdery mildew harmful?
- It weakens the plant by blocking sunlight and stealing nutrients. Treat it early to keep your hogweed healthy.
- Can I use household soap to clean the leaves?
- A very mild solution of water and a drop of dish soap can work, but be sure to rinse it off gently afterward.
More problems with Common hogweed
Back to the Common hogweed guide
This article was generated with AI from the plant’s care profile and is general information, not horticultural advice. Read about how we build these guides.