Black leaves on a magnolia tree are usually sooty mold, a dark fungal growth that develops on the sticky honeydew left behind by scale insects, rather than a disease that infects the leaf tissue itself.

What Causes the Sticky Residue That Sooty Mold Grows On?

Magnolia scale is the insect responsible, feeding on sap through small, shell-like coverings on the bark and branches and excreting the sweet, sticky honeydew that drips onto the leaves below. Sooty mold then colonizes that honeydew residue, turning the coated leaf surface black.

Does Sooty Mold Damage the Magnolia Tree Itself?

No. Sooty mold grows only on the surface of the leaf rather than infecting the plant tissue underneath, so it doesn't directly harm the tree the way a true fungal disease would. A heavy coating can block enough sunlight to reduce a leaf's ability to photosynthesize, which becomes more of a concern on a tree already stressed by a large scale infestation.

How Is Black Sooty Mold Removed From Magnolia Leaves?

Sooty mold doesn't need direct treatment since it doesn't infect the leaf, and it typically wears off on its own with rain and time once the honeydew source is gone. Controlling the magnolia scale itself is what actually stops new sooty mold from forming, since removing the insect removes what's producing the honeydew in the first place; Horticultural Oil Insect Spray, applied to the trunk and branches during the growing or dormant season, is the product used for that control.

Frequently Asked Questions

How much does treating magnolia scale to stop sooty mold cost?

$13.95 for one pint of Horticultural Oil Insect Spray, the product that controls the magnolia scale causing the honeydew.

Can black leaves be wiped or washed off by hand?

Yes. A damp cloth or a strong spray of water can wipe or rinse sooty mold off smaller plants or reachable leaves, though it keeps returning until the scale insects producing the honeydew are controlled.

Does sooty mold affect the magnolia's flowers?

Rarely. Sooty mold mainly settles on leaf surfaces below where scale insects are feeding, so flowers are usually affected only if honeydew drips directly onto open blooms.

Can sooty mold spread from a magnolia to other nearby plants?

Yes. Honeydew and the sooty mold that grows on it can land on any plant beneath or near an infested magnolia, so nearby plants may show the same black coating even though the scale insects themselves stay on the magnolia.