Pocket Botanist
Check these first
- Inspect the undersides of the leaves for fungal spores.
- Clear away all debris from the base of the tree.
- Check if the tree is crowded by other plants.
Likely causes
Anthracnose
Most likelyHow to tell: You will see irregular brown or black spots on the leaves, sometimes with a yellow halo. In severe cases, the leaves might curl or drop early.
What to do: Prune away the infected branches to improve airflow through the canopy. Clean up all fallen leaves from the ground to prevent the fungus from overwintering. Avoid overhead watering to keep the foliage dry.
Leaf Spot Fungi
PossibleHow to tell: These appear as small, distinct circular spots that may merge over time. They are most common during humid, rainy spells.
What to do: Ensure the tree has enough space between it and other plants for good air circulation. Remove and destroy any heavily infected leaves. Apply a copper based fungicide if the infection is widespread.
Find out what's wrong with your common alder
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 normal to see a few spots late in the season as leaves age. Worry if the spots cover most of the foliage or cause premature leaf drop.
Stopping it coming back
Keep the area around the tree clean and ensure it has plenty of space for air to move through the branches.
Common Alder: spots? Check yours with a photo
Every plant is a little different. Take a photo of your common alder 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.
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Questions people ask
- Will these spots kill my tree?
- Usually no, but they can weaken the tree if they happen every year. Keep the tree healthy with proper water and mulch.
- Should I spray my tree with chemicals?
- Only if the infection is severe and threatening the health of a young tree. Cultural practices like cleaning up leaves are much more effective.
Guides to these causes
More problems with Common Alder
Back to the Common Alder guide
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.