Question
i want to know how to kill bahia grass in my yard without harming the bermuda grass.

Answer
Hi Eric;
I don't think it can be done, organically or chemically, because what kills grass, kills ALL grass.
sorry I can't be of more help, but you might check with a nurseryman and find out if burmuda will eventually crowd out bahia.
I know the St. augustine varieties will crowd out burmuda.
I have no experience with Bahia.
Charlotte