Black mold on some leaves of magnolia bush

Thank you for writing.
Although you did not send a picture, I am reasonably sure this is sooty mold, explained here. https://extension.unh.edu/blog/2018/07/why-are-leaves-my-magnolia-turning-black-attracting-wasps
The problem is that if it is caused by magnolia scale, this can turn into a very serious problem very quickly.
I would like a close up picture of a couple leaves and a careful search and photograph of magnolia scale.
https://hort.extension.wisc.edu/articles/magnolia-scale/

Steve Miles, Master Gardener, Hennepin County, (I am a volunteer human being: not a bot, not AI). I'm an avid gardener but not a degreed or certified horticulturist or arborist. I will do much better if you also send a photograph. I like follow-up questions. The University' garden soil tests are excellent. https://soiltest.cfans.umn.edu/testing-services/lawn-garden This is how to find a tree expert. https://extension.umn.edu/planting-and-growing-guides/how-hire-tree-care-professional A Directory of ISA certified arborists is at https://certificates.directory.isa-arbor.com/ The Minnesota Landscape Arboretum is a wonderful place to see and learn about plants that grow in Minnesota. https://mngardens.horticulture.umn.edu/minnesota-landscape-arboretum Ask a Master Gardener is a public service of the University of MInnesota's Extension Division. Please donate if we make you happy. https://give.umn.edu/gardener Replied August 17, 2026, 4:55 PM EDT

Ugh, you were spot on. Within a day, the shrub was heavily infested with magnolia scale. I pruned a few branches and tried to remove all the scale I could see.

Is there something I should spray on the magnolia shrub now?

Thank you, Laura Anderson

The Question Asker Replied August 18, 2026, 7:31 PM EDT

Sorry to hear that I was correct.
Take a garden hose, turn to the tightest most fierce jet that you can and blast them but do not blast those critters onto other magnolia.
Send me a before and after picture,

Steve Miles, Master Gardener, Hennepin County, (I am a volunteer human being: not a bot, not AI). I'm an avid gardener but not a degreed or certified horticulturist or arborist. I will do much better if you also send a photograph. I like follow-up questions. The University' garden soil tests are excellent. https://soiltest.cfans.umn.edu/testing-services/lawn-garden This is how to find a tree expert. https://extension.umn.edu/planting-and-growing-guides/how-hire-tree-care-professional A Directory of ISA certified arborists is at https://certificates.directory.isa-arbor.com/ The Minnesota Landscape Arboretum is a wonderful place to see and learn about plants that grow in Minnesota. https://mngardens.horticulture.umn.edu/minnesota-landscape-arboretum Ask a Master Gardener is a public service of the University of MInnesota's Extension Division. Please donate if we make you happy. https://give.umn.edu/gardener Replied August 18, 2026, 8:48 PM EDT

On Tuesday, August 18, 2026 at 07:48:56 PM CDT, Ask Extension wrote:

The Question Asker Replied August 29, 2026, 4:30 PM EDT

Thank you for writing back.
That is the best you can do for this season except for carefully cleaning all fallen leaves from under the plant until the ground freezes.
Best to you.

Steve Miles, Master Gardener, Hennepin County, (I am a volunteer human being: not a bot, not AI). I'm an avid gardener but not a degreed or certified horticulturist or arborist. I will do much better if you also send a photograph. I like follow-up questions. The University' garden soil tests are excellent. https://soiltest.cfans.umn.edu/testing-services/lawn-garden This is how to find a tree expert. https://extension.umn.edu/planting-and-growing-guides/how-hire-tree-care-professional A Directory of ISA certified arborists is at https://certificates.directory.isa-arbor.com/ The Minnesota Landscape Arboretum is a wonderful place to see and learn about plants that grow in Minnesota. https://mngardens.horticulture.umn.edu/minnesota-landscape-arboretum Ask a Master Gardener is a public service of the University of MInnesota's Extension Division. Please donate if we make you happy. https://give.umn.edu/gardener Replied August 29, 2026, 4:56 PM EDT

Black mold on some leaves of magnolia bush #942706

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