Tree Diseases: Magnolia Bark

Written by karen malzeke-mcdonald
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  • Introduction

    Tree Diseases: Magnolia Bark

    The magnolia family encompasses 80 different varieties of evergreen and deciduous trees. These plants thrive in well-drained locations that offer full sunlight. All members of this family are known for their hardy nature and resistance to disease pests. Despite this, however, there are still several bark diseases that the magnolia may fall prey to.

    The magnolia family includes 80 different varieties. (magnolia image by Edsweb from

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    Nectria Canker

    Nectria canker is a fungal disease that infects the bark of the magnolia tree. It is transported by fungal spores that enter the tree through existing open wounds. The bark will become discoloured at the site of infection. As the disease progresses the bark cankers and callouses, growth is stunted and branches will die back. Stressed magnolia trees are more vulnerable. With nectria canker there is no cure, only management in pruning back the plant.

    Nectria canker will cause foliage and branches to die back. (dead tree image by Deborah Durbin from

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    Wet wood

    Wet wood, also known as slime flux, is a condition where a collection of bacteria finds its way into the tree bark through open wounds and natural openings. The infected wood becomes water soaked and begins to discolour and decay. As the disease spreads the bacteria exerts a rancid odour. The bacteria "slime" that oozes from the tree can kill other vegetation on contact. Unfortunately there are no curative or preventive measures.

    Slime from an infected tree can kill healthy vegetation on contact. (wet lemon image by Cesar Andrade from

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    Armillaria Root Rot

    Armillaria root rot, also known as shoestring root rot, is a soil-borne fungus. It mostly infects drought-stressed and frost-injured magnolia trees. The fungus enters through the roots and begins decaying the fine feeder roots of the tree. It then spreads to the bark, leading to discolouration and decay. Other symptoms include growth stunt and die back. In the most severe cases the bark will ooze a white-yellow liquid. There is no cure, however, there are fungicidal preventive treatments.

    Severly infected trees will ooze liquid. (sap on the bark image by Miroslava Holasová from

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    Disease Prevention

    Most fungal bark afflictions enter through natural openings and wounds in the bark. Young magnolia trees have very thin bark that can be easily damaged. Careful attention needs to be paid to protecting the bark. Immediate treatment of any open wounds will prevent infection. Fungal diseases also may be prevented with fertilisation and attention to watering.

    The bark of a young magnolia tree is unusually thin. (shag-bark hickory bark texture, colour image by Scott Slattery from

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    Healthy care

    In addition to protecting the bark of the magnolia, providing the proper environment will promote health. Magnolia trees require partial to full sun in order to thrive. They are not too partial to the soil provided, however moderated watering is important. Always raking up dead and fallen leaves from the base of the tree will help prevent the growth of damaging fungus.

    Removing dead leaves from the base of the tree will help prevent fungal growths. (pile of autumn leaves image by R MACKAY from

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