Answer: It's really difficult to diagnose a plant problem without actually seeing it. Yellowing leaves can indicate some stress with the roots of your tree; over- or under-watering, need for fertilizer, or even a disease such as fusarium. I think your best course of action would be to take a sample of the affected leaves (and a branch or stem) to your local Cooperative Extension office for an accurate diagnosis. The specimens you take will be examined under a microscope which can reveal clues that you and I cannot see. Your local Cooperative Extension office will be listed in the white pages under "County". Best wishes with your mimosa!
Q&A Library Searching Tips