Magnolia tree has foul smell and is attracting flies.
I pruned the tree after it stopped flowering in June; now some leaves have black markings on them & it stinks so much that it is attracting flies. It is 10 years old and never had this problem before. We did have a wetter than normal spring.
Certified GKH Gardening Expert
Uh oh! This sounds like a bacterial infection, but I also see signs of a severe fungal infection as well. Wet conditions will, certainly, make this worse!
Once it is this far along, the tree will usually perish over the next few years, unfortunately. You can still attempt treatment, though.
Dolomitic lime, and wettable sulfur, when used together, can help combat and prevent soil infections. Using these once or twice per year is ideal.
Otherwise, you can try fungicide sprays for the soil, and all portions of the tree that you can reach. This article will help: https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
This article will giv eyou information on the care of Magnolia trees: https://www.gardeningknowhow.com/ornamental/trees/magnolia/magnolia-tree-care.htm
Also, I just noticed it has scale insects. This may be the feeding insect causing the sugary deposits on the leaves. You can just brush them off.
The black staining is likely to be fungus feeding on sap deposits on the leaves. Usually the deposits are from feeding insects such as aphids. If you have recently pruned it the resulting regrowth may be a little dense. If you thin it out to create a more airy crown then this helps with general health and would discourage pests.