Killing grass in alfalfa

I have a stand of alfalfa thats a few years old and has some fall panicum along with foxtail that comes up through it in the later cuttings. I plan on seeding some orchard grass into the alfalfa to make it a mixed grass field, is there anything I can use to spray for the grass yet still be able to get orchard grass drilled into it this fall?

Killing grass in alfalfa