Magnolia problems, pests, and diseases (& how to fix them)

Common Magnolia problems relate to leaf scorch, nutrient deficiencies, or fungal disease.

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Fortunately for most gardeners growing these beautiful trees, magnolias have very few problems and are relatively low-maintenance.

However, from time to time, your magnolia may suffer from one of these problems.

Magnolia has brown leaves

Magnolia denudata or White Magnolia

If the leaves of your magnolia are turning brown, it’s most likely sun scorch.

Obviously, this is more likely to occur in summer when the midday and afternoon sun is scorching.

That’s why it’s recommended that you plant your magnolias in a spot that receives morning sun but is shaded from the harsh afternoon sun.

Leaf scorch is caused by the water rapidly evaporating from the leaves.

In turn, if the plant is not receiving enough water, it’s unable to replenish the moisture quickly enough to stop the leaves from drying up and dying. 

How to fix leaf scorch on magnolias

  • Ensure your plant gets plenty of water during the hottest months.
  • If your plant is exposed to the sun for most of the day, consider supplying some afternoon shade. This is especially important for young trees. You can either erect some shade cloth over the young tree or plant taller trees or shrubs nearby that will provide afternoon shade.
  • Apply a thick layer of mulch around the base of the tree to keep the soil and the roots cooler and help to retain moisture.

Magnolia has yellow leaves

Magnolias need iron to perform photosynthesis

One of the most prominent reasons for magnolia leaves turning yellow is inadequate nutrition.

This could be caused by soil that is too alkaline. Soil that has a high pH level often binds important nutrients such as iron and makes them unavailable to the plant roots.

Apart from nitrogen, phosphorus, and potassium, iron is an important mineral that plants such as magnolias need to perform photosynthesis.

So, if the leaves are yellow with green veins, your plant may have an iron deficiency.

How to fix nutrient deficiencies in magnolia

  • Check the pH level of your soil. Magnolias prefer slightly acid soil with a pH of around 5 to 6. 
  • If your soil is too alkaline, you need to lower the pH. You can do this in a variety of ways. Adding plenty of compost and organic matter to the soil will lower the pH over time. However, you might also want to look for a more rapid solution like a liquid soil acidifier that you can find at your local garden centre or at Bunnings. These usually contain sulphur.
  • You can also get some chelated iron that you can mix with water and spray on the leaves to give your plant a boost more quickly.
  • Make sure that you feed your plant with an organic fertiliser at least twice a year in spring and autumn.

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Black spots on magnolia leaves

If your magnolia leaves are exhibiting black spots, it’s most likely due to a fungal disease.

Fungal diseases are more common in areas with high humidity and can also be a concern if you’ve had a lot of rain.

The fungal spores live in the soil and can be splashed up onto the lower branches and leaves of the tree.

How to fix black spots on your magnolia leaves

  • If the disease is widespread, you can treat it with a copper-based fungicide that you spray all over the trees.
  • You might also want to remove the diseased leaves to prevent the disease from spreading all over your tree. Make sure that you put these into the rubbish and not into your compost bin.
  • Another good practice is to remove any low branches that are close to the ground. This will reduce the potential for the fungal spores to splash up onto the foliage when it rains heavily.

Are there any pests that can attack magnolias?

Magnolias are generally pest-free

In general, magnolias have very few pest problems once they’re well established.

However, young trees may attract common garden pests such as caterpillars, aphids, and scale.

This is not all that common but if it does happen to your magnolia, there are various easy ways to treat these pests.

  • Caterpillars can simply be picked off the leaves by hand or, in severe cases, you can spray the plant with an organic insecticide.
  • Aphids and scale are best treated with an oil-based spray such as white oil.

FAQ

Why are my magnolia leaves yellowing?

Magnolia leaves turning yellow often means inadequate nutrition. This could be caused by soil that is too alkaline which makes important nutrients unavailable to the plant roots.

How do I fix yellow leaves on my magnolia tree?

Check the pH level of your soil and amend it as required. Magnolias prefer slightly acid soil with a pH of around 5 to 6. 

Photo of author

Annette Hird

Annette Hird has an Associate Diploma of Applied Science in Horticulture. She has worked in a variety of production nurseries, primarily as a propagator. She also had the responsibility of a large homestead garden that included lawn care, fruit trees, roses and many other ornamental plants. More recently, Annette has concentrated on improving the garden landscape of the homes that she has lived in and focused a lot of energy on growing edible plants as well. She now enjoys sharing her experience and knowledge with others by writing articles about all facets of gardening and growing plants.