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Common Alder · Alnus glutinosa

What are the bugs on my Common Alder?

Common Alders are prone to a few specific visitors like aphids and leaf beetles. These pests can cause distorted growth or skeletonized leaves. Check the leaves closely to see if you have an active infestation.

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pests on a plant
Photo: Jules Verne Times Two, CC BY-SA 4.0

Check these first

  1. Look for skeletonized leaves or holes.
  2. Check the undersides of new leaves for clusters of tiny bugs.
  3. Look for sticky residue on the leaves.

Likely causes

  1. Alder Leaf Beetle

    Most likely

    How to tell: You will see small metallic blue or green beetles and their larvae eating the leaf tissue. This leaves behind a skeletonized look where only the veins remain.

    What to do: Pick the beetles off by hand if the tree is small. For larger infestations, use a strong stream of water to knock them off. You can also use neem oil if the damage is extensive.

  2. Aphids

    Possible

    How to tell: These tiny insects cluster on new growth and the undersides of leaves. They leave behind a sticky substance called honeydew.

    What to do: Spray the tree with a steady stream of water to dislodge the aphids. Introduce beneficial insects like ladybugs to your garden. Use insecticidal soap if the population is out of control.

Pests on other plants

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

Small numbers of pests are usually handled by nature. Worry if the tree is losing a significant amount of its leaves or if growth is severely stunted.

Stopping it coming back

Encourage natural predators like ladybugs and lacewings by planting a variety of flowers nearby.

Common Alder: pests? 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 the beetles kill my tree?
They rarely kill a mature tree, but they can make it look quite ragged. Keep the tree well watered to help it recover from the stress.
Is the sticky stuff on my leaves harmful?
That is honeydew from aphids, and it can lead to sooty mold. Wash it off with water to keep the leaves clean and healthy.

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.