Eastern Redbud alba – leaves started to turn yellow and falling in July.

Question

Now remaining leaves have dark patches which look llike a fungus? neighboring (not alba) redbuds seem fine.

Answer 1

Your redbud may be suffering from verticillium wilt, which is not good news. Here are two articles to help you understand and deal with this fungal disease:
https://www.gardeningknowhow.com/plant-problems/disease/verticillium-wilt-treatment.htm
https://ag.purdue.edu/btny/ppdl/Pages/WH_old/hot08/8-7.html

You may want to take a sample of a small branch to your closest extension service agent to be sure. Here's the info for you: https://www.gardeningknowhow.com/extension-search?zip=65559&radius=50&services_search_action=search&submit=Search