Is the white powder harmful to touch?

The powder itself is just fungus, but remember that Giant Hogweed sap is toxic and causes severe burns. Always wear gloves and long sleeves when working near this plant.

Will the spots kill my plant?

Powdery mildew rarely kills a healthy, established Giant Hogweed. It mostly makes the plant look unsightly and can weaken it over time.

Giant Hogweed: spots, causes and fixes

Check these first

Rub the white spot with your finger to see if it comes off as powder.
Inspect the underside of the leaves for any insects.
Check if the spots are appearing mostly on the upper leaves.

Likely causes

Powdery Mildew
Most likely
How to tell: You will see a white, flour like coating on the surface of the leaves. It often starts as small patches and spreads quickly in humid weather.
What to do: Remove the most heavily infected leaves to stop the spread. Apply a mixture of one tablespoon of baking soda to a gallon of water as a mild fungicide. Ensure you have good air circulation around the plant to keep foliage dry.
Sunscald
Possible
How to tell: These spots look like bleached or papery patches on leaves that get intense afternoon sun. They do not rub off like fungus.
What to do: Provide some shade during the hottest part of the day if the plant is in a very exposed spot. Keep the soil moist so the plant can handle the heat better.

Leaf spots on other plants

Find out what's wrong with your giant hogweed

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

If the spots cover most of the foliage and the leaves begin to shrivel, the plant is struggling significantly. Minor spotting on older leaves is common in late summer.

Stopping it coming back

Water at the base of the plant to keep the leaves dry and maintain enough space between plants for airflow.

Giant Hogweed: spots? Check yours with a photo

Every plant is a little different. Take a photo of your giant hogweed 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 the white powder harmful to touch?: The powder itself is just fungus, but remember that Giant Hogweed sap is toxic and causes severe burns. Always wear gloves and long sleeves when working near this plant.
Will the spots kill my plant?: Powdery mildew rarely kills a healthy, established Giant Hogweed. It mostly makes the plant look unsightly and can weaken it over time.

Guides to these causes

Powdery Mildew

Why are there white spots on my Giant Hogweed leaves?

Check these first

Not sure what's wrong with your giant hogweed?