Magnolia Tree Fungus: 11 Fungal Diseases & Treatment

by Jamie

The magnificent magnolia, known for its beautiful flowers and durable foliage, is a common feature in numerous gardens. However, like all trees, magnolias are prone to different diseases, especially those caused by fungi.

Although fungi are the predominant pathogens, it’s worth noting that magnolia diseases may also arise from bacterial sources.

Key Takeaways

Magnolias, while stunning, are susceptible to various fungal and bacterial diseases.
Timely intervention, like pruning and fungicide application, can manage most diseases.
Proper care, including appropriate watering and ensuring good air circulation, can prevent many diseases.
When in doubt, consulting a certified arborist can provide guidance on keeping magnolia trees in optimal health.

Unfortunately, a fungal issue is not the only problem that can occur with a magnolia tree. In my detailed guide, Magnolia Tree Diseases, Pests, and Problems, I fully cover more than 30 possible issues and how to fix them. It’s a must-read!

1. Black Sooty Mold

Black sooty mold is a common magnolia tree disease. This fungus manifests as a black, powdery substance that covers the leaves and branches of the magnolia tree.

While it doesn’t directly harm the magnolia leaf, it can block sunlight, hindering the tree’s photosynthesis process.

Identifying Characteristics:

Presence of a black, powdery layer on the magnolia leaf.
Often accompanied by an infestation of pests, such as aphids or scale insects, that excrete a sticky substance known as honeydew, on which the mold thrives.

Effects on the Tree:

Reduced photosynthesis due to the blocking of sunlight.
Leaves may turn yellow and fall prematurely.
Aesthetically, the tree may lose its vibrant green leaves, affecting its ornamental value.

Treatment:

Regularly check for pests on the magnolia tree, and use pest control measures.
Gently spray the magnolia leaves with a mixture of water and mild soap to break down the mold.
For severe infestations, consult with a certified arborist or a company offering residential tree services for professional treatment.

2. Verticillium Wilt

Verticillium wilt is a soil-borne fungal disease that infests the magnolia tree through wounds, primarily in the roots.

The fungus blocks the tree’s vascular system, restricting the flow of water and nutrients.

Identifying Characteristics:

Wilting and yellowing of leaves, despite adequate watering.
Leaves and branches may turn reddish-brown.
A cut through the magnolia tree’s trunk and branches may reveal dark streaks in the wood.

Effects on the Tree:

Older trees might show stunted growth.
Leaves may droop, turn yellow, or fall off.
If untreated, verticillium wilt can kill the tree.

Treatment:

Prune diseased branches, and dispose of them properly to prevent the fungus from spreading.
Ensure proper irrigation, and avoid waterlogging around the magnolia tree.
Apply a balanced fertilizer to strengthen the tree against diseases.
Ensure adequate air movement around the tree to discourage fungal growth.
For prevention, avoid planting magnolias in soil previously infested with the verticillium wilt pathogen.

3. Cankers

Cankers are dead sections on the bark of magnolia trees often caused by fungal or bacterial pathogens. They form as sunken, dark areas on the bark and can expand over time.

Identifying Characteristics:

Sunken, dark lesions on the bark, which can be oval or elongated.
Foliage above the canker may wilt or turn yellow.
The canker might produce a gummy or sap-like substance.

Effects on the Tree:

Cankers interrupt the flow of nutrients in the affected area, causing branches above the canker to weaken or die.
In severe cases, canker diseases may girdle the tree, leading to death.
Affected magnolia trees may become more susceptible to other diseases and pests.

Treatment:

Prune away the affected branches well below the cankered areas and dispose of them to prevent the spread of the pathogen.
Ensure that the magnolia tree remains healthy with proper watering and fertilizing schedules.
Avoid wounding the tree as open wounds can become entry points for the pathogens causing canker.
Apply fungicide or bacterial sprays as a preventive measure, especially during humid conditions.

4. Leaf Spot Disease

Leaf spot on magnolia trees is a common fungal disease characterized by small, round, brown spots on the foliage.

This fungus primarily targets the magnolia leaf during wet conditions.

Identifying Characteristics:

The presence of brown leaf spots, often surrounded by a yellow halo.
The spots can merge, creating larger blotchy areas on the leaves.
In severe cases, the leaf spot disease can cause premature leaf drop.

Effects on the Tree:

Reduced photosynthesis, which can stunt growth.
Aesthetic decline, diminishing the ornamental value of the magnolia.
Weakening of the tree, making it susceptible to other diseases and pests.

Treatment:

Prune and dispose of infected leaves to prevent the spread of the fungus.
Improve air circulation by spacing trees and shrubs properly and thinning out dense foliage.
Apply a fungicide spray like this one as a preventive measure, especially during humid weather.

5. Algal Leaf Spot

Unlike the typical fungal leaf spots, algal leaf spot is caused by an algal pathogen. This disease manifests as raised, rough spots on the leaves of magnolia trees.

Identifying Characteristics:

Raised, velvety green spots that turn gray over time.
The spots can be seen on both sides of the magnolia leaf.
Hair-like structures on the undersides of the spots.

Effects on the Tree:

Can cause minor defoliation in severely infected trees.
Reduces the aesthetic value of the magnolia tree due to the presence of the unsightly spots.
Rarely fatal but can weaken the magnolia, making it more susceptible to other issues.

Treatment:

Prune away heavily infested leaves, and dispose of them properly.
Encourage better air movement around the tree to prevent the moist conditions favored by the algal pathogens.
Fungicides that target algal pathogens can be used, but always consult with an arborist before application.

6. Anthracnose

Anthracnose is a serious disease caused by a fungus that affects many species of trees, including magnolias. The disease primarily targets the leaves, twigs, and branches of the magnolia tree.

Identifying Characteristics:

Dark, sunken lesions on leaves that may enlarge and form dead areas.
Twig dieback, where the tips of twigs blacken and die.
Reddish-brown discoloration on the trunk and branches.

Effects on the Tree:

Defoliation, especially in young magnolia trees.
Reduced growth and vitality.
Dieback of branches and twigs affects the overall structure and health of the tree.

Treatment:

Infected leaves, twigs, and branches should be pruned and disposed of properly.
Ensure adequate spacing between trees to reduce humidity and improve air circulation.
Fungicides can be effective, especially when applied early in the infection. Consult with a certified arborist for recommendations.

7. Wetwood

Also known as slime flux, wetwood is a bacterial disease affecting many tree species, including the magnolia.

It causes a foul-smelling, sticky liquid to ooze from the trunk or branches of the magnolia tree.

Identifying Characteristics:

Wet, weeping areas on the trunk or branches.
A foul odor emanating from the liquid.
Discoloration of the bark surrounding the ooze.

Effects on the Tree:

The magnolia tree’s overall vigor and health may decline.
Increased susceptibility to fungal infestations due to the wet areas.
The disease itself is rarely fatal but can weaken the tree, making it more prone to other diseases and pests.

Treatment:

There’s no definitive treatment for wetwood. However, maintaining the overall health of the magnolia is key.
Avoid injuring the tree because wounds can become entry points for bacteria.
A certified arborist might suggest drilling to relieve pressure or applying certain treatments to affected areas, but these methods have varying success rates.

8. Wood Decay

Wood rot, or wood decay, is caused by various fungi that break down the cellulose and lignin in the wood. This leads to structural weakness in the affected magnolia tree.

Identifying Characteristics:

Soft, crumbly, or spongy wood on the trunk, branches, or roots.
Presence of fungal fruiting bodies, like mushrooms or conks, on or near the tree.
Hollow sounds when tapping on the trunk or branches.

Effects on the Tree:

The structural integrity of the magnolia tree is compromised.
Increased risk of branches or even the entire tree collapsing.
The tree’s ability to transport water and nutrients can be hindered.

Treatment:

Prune and dispose of diseased branches or sections to prevent further spread.
Ensure proper watering, and avoid causing injuries to the tree because open wounds can be entry points for fungi.
Fungicides are rarely effective for wood decay. Instead, consult a certified arborist to assess the tree’s condition and recommend appropriate actions.

9. Powdery Mildew

Powdery mildew is a common magnolia tree disease caused by several different fungi. It forms a white, powdery substance on the leaves and stems of the magnolia.

Identifying Characteristics:

White to gray powdery spots or patches on the magnolia leaves, twigs, and sometimes flowers.
Infected leaves may curl, twist, or become discolored.
Over time, the white patches may turn yellowish-brown, and the infected leaves might drop prematurely.

Effects on the Tree:

Reduced photosynthesis due to the covering of the fungus on magnolia leaves leads to stunted growth.
Aesthetic decline as the tree appears “dusty” or “moldy.”
While rarely fatal, the disease can weaken the tree and make it more susceptible to other issues.

Treatment:

Prune affected areas, and improve air circulation around the tree by thinning dense foliage.
Apply fungicide sprays early in the disease’s development. These can be effective if used appropriately.
Water the magnolia at the base rather than overhead to keep leaves dry and reduce favorable conditions for the fungus.

10. Root Rot Fungus

Root rot, predominantly caused by fungi, is a severe magnolia tree disease that targets the roots.

Often a consequence of prolonged soil saturation, the fungi compromise the tree’s ability to absorb water and nutrients.

Identifying Characteristics:

Yellowing or wilting of the magnolia leaves that isn’t alleviated with watering.
Reduced growth and vigor of the magnolia tree.
Mushrooms or fungal structures near the base of the tree.
Decaying roots when inspected.

Effects on the Tree:

Progressed stages of this disease can kill the tree.
Hindered ability to absorb water and nutrients, resulting in visible stress on the tree.
Structural instability as root systems decay.

Treatment:

Ensure proper soil drainage around the magnolia to avoid waterlogging.
Prune and dispose of infected roots. However, this is a challenging task and is best done under the guidance of a certified arborist.
Fungicides may be helpful but are often more effective as a preventive measure rather than a cure.

11. Rust

Rust is a fungal disease affecting various plants, including the magnolia. It’s named for its distinctive rust-colored spores that appear on the magnolia leaves.

Identifying Characteristics:

Bright orange, rust-colored pustules on the underside of the magnolia leaf.
Yellowing and eventual browning of infected areas.
Premature leaf drop in severe cases.

Effects on the Tree:

Reduced photosynthesis due to damaged foliage leads to stunted growth.
Severe infections can weaken the magnolia, making it more susceptible to other diseases and pests.
Aesthetic decline, given the unsightly appearance of rusted leaves.

Treatment:

Prune and dispose of infected magnolia leaves to prevent the spread of the fungus.
Fungicide sprays can be effective against rust, especially when applied early. Always follow the product recommendations, and consult with a certified arborist if unsure.
Improve air circulation around the tree by spacing out trees and shrubs or thinning dense foliage to reduce humidity levels.

Final Thoughts About Magnolia Tree Fungus

In conclusion, while magnolias are majestic and beautiful, they are not immune to fungal diseases.

Regular inspection, prompt action, and preventive measures can mitigate the risk and ensure your magnolia remains a focal point in your garden for years to come.

If you ever doubt the health of your magnolia, reaching out to professionals or certified arborists is a wise step.

Now that you’re up to date on magnolia fungus problems, head over to these guides next to learn about common leaf issues: