Are these pests going to kill my plant?

Usually not, but they can weaken it significantly. Catching them early is the key to keeping the plant vigorous.

Can I use chemical pesticides?

It is better to avoid harsh chemicals to protect beneficial insects like bees that love thistle flowers. Stick to water or insecticidal soap.

What are those pests on my Scotch Thistle? Causes and fixes

Check these first

Inspect the undersides of the leaves with a magnifying glass.
Look for sticky residue or webbing on the stems.
Check if the plant looks dehydrated or dusty.

Likely causes

Aphids
Most likely
How to tell: Small green or black insects clustered on the new growth or flower buds.
What to do: Spray the plant with a strong stream of water to knock them off. If they persist, use a mild insecticidal soap once a week until they are gone.
Spider mites
Possible
How to tell: Fine webbing between leaves and tiny yellow dots on the foliage.
What to do: Increase humidity around the plant if possible and spray the leaves with water. Use neem oil if the infestation is heavy, applying it in the evening to avoid leaf burn.

Pests on other plants

Find out what's wrong with your cotton thistle

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 leaves start turning yellow or curling due to heavy feeding, you need to treat the plant immediately. A few bugs are usually manageable.

Stopping it coming back

Keep the plant healthy with consistent water during dry spells and avoid excessive nitrogen fertilizer, which attracts aphids.

Cotton thistle: pests? Check yours with a photo

Every plant is a little different. Take a photo of your cotton thistle 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

Are these pests going to kill my plant?: Usually not, but they can weaken it significantly. Catching them early is the key to keeping the plant vigorous.
Can I use chemical pesticides?: It is better to avoid harsh chemicals to protect beneficial insects like bees that love thistle flowers. Stick to water or insecticidal soap.

What are those pests on my Scotch Thistle?

Check these first

Likely causes

Aphids

Spider mites

Find out what's wrong with your cotton thistle

When to worry

Stopping it coming back

Cotton thistle: pests? Check yours with a photo

Questions people ask

Guides to these causes

More problems with Cotton thistle