Pocket Botanist
Check these first
- Inspect the undersides of the leaves for powdery spores.
- Check if the spots have a yellow halo around them.
- Look for fallen leaves that might be harboring fungus.
Likely causes
Leaf Rust
Most likelyHow to tell: You will see small orange or yellow spots on the leaf surface and dusty spores on the underside.
What to do: Remove and destroy all fallen leaves to stop spores from spreading. If the infection is severe, apply a copper based fungicide spray according to the label instructions.
Septoria Leaf Spot
PossibleHow to tell: These spots are usually brown or black with a yellow halo around them.
What to do: Prune away heavily infected branches to improve airflow through the canopy. Keep the area around the base of the tree clear of debris.
Find out what's wrong with your cottonwood
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.
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When to worry
It is rarely fatal for a mature tree, but it can weaken young saplings if they lose too many leaves early in the season.
Stopping it coming back
Keep the area under the tree clean and ensure there is enough space between trees for good air circulation.
Cottonwood: spots? Check yours with a photo
Every plant is a little different. Take a photo of your cottonwood 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.
Scan with your phone's camera to get the app
Or go to pocketbotanist.app/get on your phone
Get the app · Or check it from a photo now, free
Questions people ask
- Will these spots kill my tree?
- Usually no, but it can cause premature leaf drop which stresses the tree.
- Should I water the leaves to wash the spots off?
- No, avoid overhead watering as wet foliage encourages fungal growth.
Guides to these causes
More problems with Cottonwood
This article was generated with AI on from the plant’s care profile and is general information, not horticultural advice. Read about how we build these guides.