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8 Most Common Magnolia Tree Diseases With Photos

Magnolias have always been highly sought-after trees in the yard. However, like all organisms on earth, they tend to get sick. Today we will look at the most common magnolia diseases and how to treat them.

Disease Symptoms Treatment
Leaf spot Brown spots on the leaves. Spray magnolia with copper fungicide.
Powdery mildew White powder on the leaves. Spray the leaves with horticultural oil.
Algal leaf spot Gray rounded spots. Spray the leaves with fungicide.
Bacterial blight Dark angular spots. Remove damaged leaves.
Crown gall Large outgrowths on the branches. Cut back the branch below the damage.
Wetwood Wounds in the trunk from which fluid oozes. Cut out the gall with a sharp knife.
Wood decay Wounds on the trunk in which there is rotten wood. Clean the wound of dead wood and wash it with alcohol.
Canker Cracks and growths on the trunk and branches. Clean the wound of dead wood and wash it with fungicide.

Fungus leaf spot

magnolia diseases leaf spot

Fungus leaf spot

A fairly large variety of pathogens can cause magnolia leaf disease. As a result, their appearance is severely damaged, although it is rarely fatal to the tree.

Usually in spring, when the weather is warm and humid, the pathogens settle on young leaves and begin to germinate. Over time, this spot becomes increasingly pale until the tissue dies and a brown spot appears.

If the leaf is heavily infested, there can be so many spots that they create a large brown area on the leaf. Such leaves usually die after a while.


The first thing to do is to remove leaves that are more than half brown. Collect all of the fallen leaves around the magnolia. Throw away any damaged leaves far away from the yard.

Spray the leaves and petioles with an aqueous solution of copper fungicide. Repeat the spraying in two weeks.

Avoid overwatering the magnolia and allow the soil to dry out a little between waterings. When watering, be careful not to drip onto the leaves. Ensure good air movement around the crown.

Read more: How do you keep magnolias healthy?

Powdery mildew

how to treat magnolia disease

Powdery mildew

Powdery mildew is a fungal disease that affects magnolia leaves. If you notice it in time and treat it, nothing terrible will happen. However, young trees can be severely damaged if the disease is noticed too late.

The disease is most active during the warm summer months. A white substance that resembles powder appears on the leaves. The leaf may darken or turn brownish green.


The easiest and most effective way to treat powdery mildew is to spray magnolia leaves and branches with an aqueous solution of horticultural oil. Although this product is designed for pest control, it does a good job with powdery mildew as well.

Another way is to spray the leaves with an aqueous solution of a systemic fungicide. A product that contains myclobutanil works best.

Algal leaf spot

magnolia tree leaf disease

Algal leaf spot

Algal leaf spot is a disease that affects trees and shrubs with thin, leathery leaves. It is a disease that quite severely spoils the appearance of the bright green leaves of magnolia trees.

Like most such diseases, the Algal leaf spot is most active in warm and humid weather. Pathogens settle on the leaves and begin to destroy them.

As a result, light gray spots appear on the leaf blade about half an inch across. The spots often have something like flakes on them.


Tear off leaves that have more than four or five spots on them. Collect the fallen leaves from underneath the magnolia. Throw away all this debris as far away from the garden as possible.

Spray the leaves, petioles, and branches with an aqueous solution of copper fungicide. Repeat the spraying in 7 to 10 days.

Try to keep the water droplets away from the leaves while watering. Avoid keeping the ground around the magnolia constantly moist.

Bacterial blight

magnolia tree diseases

Bacterial blight

Bacterial blight damages the young leaves of many plants, including magnolias. Older leaves are usually untouched by this disease.

When the weather changes to rainy and stormy conditions are ideal for this disease to develop. Bacterial blight prefers cool and humid conditions best.

Faint watery spots appear on the leaves at first. Over time, they will turn dark brown. They are not round, but angular or irregular in shape. After a while, a hole may appear in the center of the spot.


Cut all diseased foliage from the tree and collect the fallen leaves. Throw it all in the trash or burn it.

The only chemical that can control this disease is a copper fungicide. Use it several times at 1-2 week intervals.


magnolia tree common diseases

Slime flux

Wetwood is a disease that affects the trunk and branches of magnolia trees. There are several types of bacteria that cause this disease. They enter the tree through wounds or cracks in the bark.

After a while, fluid begins to ooze out of the area where the disease is. Often it will dry out on the stem and have a whitish color.


If the infestation is on the branch, cut it off below the affected area. Always use a sterile pruning tool. Try to do the pruning in dry weather so that the wound dries up quickly.

If the sore is on the trunk, carefully clean it with a sharp knife. Take care not to damage any living tissue.

Spray the wound with alcohol; you can even pour some alcohol into the wound. Alcohol can kill bacteria and reduce the activity of the disease. Repeat this after 1-2 months.

Water the magnolia with liquid fertilizer to give it the strength to fight the disease. All of these actions together greatly increase the magnolia’s chances of recovery.

Crown gall

disease magnolia tree

Agrobacterium tumefaciens

Agrobacterium tumefaciens is a bacterium that causes a disease called crown gall. Many different plants are susceptible to this disease, including magnolias.

The pathogen enters the tree through damage (wounds, cracks, etc.). The disease results in large growths on the tree that are much larger than the branch or trunk on which they are growing.

In general, the tree rarely dies from this disease. It is most dangerous for young trees. If the gall grows around the trunk, the sap flow can be interrupted and the tree will die.


Try to keep your magnolia tree undamaged. Always disinfect tools when pruning.

Remove the gall with a sharp, sterile knife. Cut it very carefully to avoid damaging healthy tissue. Do this in dry weather so that the wound dries quickly and stays that way for at least a few days.

If the gall has formed on a side branch, cut it off a little below this spot.

Wood decay

diseased magnolia

Wood decay

Wood decay is a rather serious disease that affects the trunk of the tree. It usually affects older trees.

The pathogens get into cracks in the bark or where the trunk and branch come together. Then they begin to develop and destroy the tissues of the tree. In the place where there are many of them appears rotten wood.


Clean the wound of dead tissue. Avoid damaging the living part of the tree and use a sharp tool.

Spray the wound with copper fungicide and when it is dry, spray again with alcohol. Afterward, feed the tree with a multi-purpose fertilizer.

If wood decay progresses, use the services of a tree treatment company.


diseases that affect magnolia trees


Canker damages the trunk and branches of the tree. As a result, the leaves above the wound begin to turn yellow and fall off.

Symptoms are bark deformation in the place where the disease is developing. Also black necroses appear in the most severely affected places.

This is a rather serious disease that can lead to the death of the tree if left untreated.


Remove all dead tissue with sharp and sterile tools. Spray the wounds with an aqueous fungicide solution. Do all this work while it is dry.

If the disease has affected the branch, cut it off a little closer to the trunk.