Answer: I can't be sure without seeing the plant, but what you describe sounds like bacterial blight (which is common in magnolias and other ornamental shrubs). If so, you may be able to control it with a fall spray of copper. Before treating your tree, though, why not take a sample of the affected leaves and flowers to your local Cooperative Extension office or Master Gardener clinic for positive identification of the problem? Helpful folks there will be able to offer some control measures. Best wishes with your magnolia!
Q&A Library Searching Tips