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Star magnolia · Magnolia stellata

What are these bumps on my Star magnolia branches?

If you see strange, waxy bumps on the stems of your Star magnolia, you are likely dealing with magnolia scale. These insects suck the sap from your tree and can cause significant stress if left unchecked.

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

Check these first

  1. Look closely at the stems for raised, waxy bumps.
  2. Check the leaves for a sticky residue or a black, powdery coating.
  3. Observe if ants are crawling on the branches, as they often feed on the honeydew.

Likely causes

  1. Magnolia Scale

    Most likely

    How to tell: You will see large, soft, brownish bumps on the branches that look like small shells. You might also notice a sticky substance called honeydew on the leaves or black sooty mold growing underneath.

    What to do: Scrape off the scales by hand in late summer or early fall when they are most active. Apply a horticultural oil spray during the dormant season to smother any remaining eggs or crawlers.

  2. Sooty Mold

    Possible

    How to tell: A black, powdery coating appears on the leaves, which is actually a fungus growing on the sugary waste left behind by scale insects. The mold itself does not hurt the tree, but it blocks sunlight.

    What to do: Treat the underlying scale infestation first, as the mold will disappear once the insects are gone. You can gently wash the leaves with a mild soap solution to remove the existing mold.

Pests on other plants

Find out what's wrong with your star magnolia

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

You should worry if the scale covers a large portion of the branches or if the tree shows signs of stunted growth. A light infestation is manageable, but a heavy one can kill branches.

Stopping it coming back

Monitor your tree regularly during the summer and keep it healthy with proper watering so it can resist pest pressure.

Star magnolia: pests? Check yours with a photo

Every plant is a little different. Take a photo of your star magnolia 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

Can I just wash the scale off with a hose?
A strong stream of water can help remove some, but it is usually not enough to get rid of a full infestation. Manual removal or horticultural oil is more effective.
Will the black mold hurt my tree?
The mold itself is just a fungus feeding on the honeydew left by the scale insects, but it shades the leaves and reduces the tree's ability to make food. It is a clear sign that you have a pest problem to address.

Guides to these causes

More problems with Star magnolia

Back to the Star magnolia 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.