Medal (S-metolachlor) does not control emerged weeds. You need to have it on before weeds emerge.

So, the question(s) is/are:  is your current program giving you season-long weed control?  or is it running out of steam before the end of the growing season?  Are you getting weeds breaking thru late?  if weeds are breaking late, what kind of weeds are they?  (will the Medal help with later-emerging weeds?

and... what is your row spacing?  30" ?  15" ?  or ????