Skip to Content

12 Most Common Magnolia Tree Diseases With Images

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.
Verticillium wilt Leaf wilting. Cut off branches that are damaged by the disease.
Algal leaf spot Gray rounded spots. Spray the leaves with fungicide.
Bacterial blight Dark angular spots. Remove damaged leaves.
Sooty Mold The leaves are covered with a black, sticky substance. Spray the magnolia with a systemic insecticide.
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.
Chlorosis Leaves turn yellow but the veins remain green. Acidify the soil and fertilize every year.
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.
Root Rot Yellowing of leaves. Eliminate the cause of the overwatered soil.

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.

Symptoms

  1. Brown spots on leaves.
  2. Leaf yellowing.
  3. Leaf drop.

Treatment

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.

Symptoms

  1. Leaves turn dark.
  2. White coating appears on the leaves.
  3. Leaves fall off.

Treatment

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.

Verticillium wilt

magnolia diseases verticillium wilt

Verticillium Wilt

The pathogens of this disease are Verticillium dahliae and Verticillium albo-atrum. Usually the spores are found in the soil and under favorable conditions begin to attack the magnolia.

The disease penetrates through wounds or cracks in the bark and infects the tissues that are responsible for the movement of sap in the trunk and branches. Over time, the branches die back.

Symptoms

  1. Leaf wilting.
  2. Yellowing of leaves on infected branches.
  3. Stunted growth.
  4. Dark spots on the bark of infected branches.
  5. Branch dieback.

Treatment

As of today, there are no effective chemicals to cure magnolia from Verticillium wilt. However, you can do some things that can remedy the situation.

Cut off branches that are damaged by the disease. Use sterile tools and disinfect them after use.

Treat wounds after pruning with a multipurpose fungicide. Allow the wound to dry and do not wrap it with anything.

Avoid mechanical damage to the trunk and branches, especially in winter. If the plant is damaged, treat the wound with multipurpose or copper fungicide.

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.

Symptoms

  1. Light gray spots appear on the leaf blade about half an inch across.
  2. The spots have something like flakes on them.

Treatment

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.

Symptoms

  1. Faint watery spots appear on the leaves.
  2. Spots turn dark brown.
  3. The spots are turning into holes.

Treatment

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.

Sooty Mold

magnolia diseases sooty mold

Sooty Mold

Although it is a fungal disease, it is caused by insects. It starts with aphids forming colonies on the leaves and petioles of the magnolia. In the process of their vital activity, they release sticky honeydew that falls on the lower leaves.

Some species of fungus parasitize these secretions without damaging the leaf itself. However, such a leaf may fall off due to lack of light which blocks the fungus.

Symptoms

  1. The leaves are covered with a black, sticky substance.
  2. In case of heavy infestation, the magnolia slows down its growth.
  3. Aphids are present on the upper leaves.

Treatment

Spray the magnolia with a systemic insecticide or horticultural oil to get rid of aphids. Make sure the product you use can be applied to the magnolia.

There is no point in treating leaves that are already infected with fungus. It is best to remove them to prevent the fungus from spreading.

Water the magnolia with liquid fertilizer to give it some energy to recover.

Keep a constant eye on the tree for aphids. As soon as you see aphids, wash them off with a hose before the colony grows. This will avoid the use of chemicals.

Wetwood

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.

Symptoms

  1. Cracks in the bark.
  2. White liquid oozes from bark cracks or just from the bark.

Treatment

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.

Symptoms

  1. Wounds on the trunk or branches of a magnolia tree.
  2. Large lumps on the trunk or branches of the magnolia.

Treatment

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.

Chlorosis

magnolia tree diseases chlorosis

Chlorosis

Chlorosis is a disease caused by mineral deficiencies. It is usually iron or magnesium deficiency. As a result, photosynthesis becomes impossible and leaves become discolored.

There are several reasons why magnolia trees experience mineral deficiencies. In most cases it is due to poor soil. However, sometimes the soil can be too alkaline and the magnolia is simply unable to absorb minerals from it.

Another cause can be overwatering and as a consequence root rot. The roots are simply not able to work properly, which affects the appearance of the magnolia.

Symptoms

  1. Leaves turn yellow but the veins remain green.
  2. The tree noticeably slows down its growth.
  3. Severely yellowed leaves fall off.

Treatment

Check the pH of the soil and if it is above 7.0 you need to lower the pH. To do this, use garden sulfur or another acidifier following the manufacturer’s recommendations. Also mulch the magnolia with organic matter. Organics can also lower the pH of the soil.

Apply a slow-release, multi-purpose fertilizer every spring. Make sure it contains nitrogen, phosphorus, potassium, magnesium, iron and zinc.

If root rot is the cause of chlorosis, water the magnolia only when the soil is 2 inches dry. Make sure there is no roof water leaking into the area where the magnolia is growing and if so, correct it.

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.

Symptoms

  1. Cracks and wounds in the bark.
  2. The bark rots in places of cracking.
  3. Bark discoloration in affected areas.

Treatment

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.

Canker

diseases that affect magnolia trees

Canker

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.

Symptoms

  1. Deformation of the bark in the affected areas.
  2. Blackening of bark in affected areas.
  3. Wounds in the bark.

Treatment

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.

Root Rot

magnolia diseases root rot

Root Rot

This is a very serious disease that affects the roots. If it attacks the magnolia, the roots begin to rot, which can lead to the death of the tree.

The cause of root rot in most cases is too wet soil. Excessive soil moisture can be caused by frequent watering, poorly drained soil, or an improperly chosen planting site.

Symptoms

  1. Yellowing of leaves.
  2. Large brown spots on the leaves.
  3. Leaf fall.
  4. Drying of magnolia branches.
  5. Stopping growth.

Treatment

Eliminate the cause of the overwatered soil. If the cause of wet soil is too frequent watering, allow the soil to dry out 2 inches between waterings.

Make sure the magnolia is not planted where rainwater flows or collects. If so, direct the water away or transplant the magnolia to a less wet location.

Leana

Saturday 18th of November 2023

My magnolia only had 3 flowers on its lowest branches this spring. It should now be in full leaf,but only the lowest branches have full leaves the rest of the tree looks like it’s trying to grow leaves but they are stumpy leaves only. The tree is 29years old & is usually a beautiful display. I’m worried about it, does anyone have any idea what could be wrong?