Surestart can be applied on corn up to 11" tall.  I don't recall if you are no-till, or if you work ground.   A good starting point could be 1 qt/acre glyphosate + 1 quart/acre Surestart applied to corn at 6".  Now, depending on your tillage program, you can decide what you need to add to that - pre-emerge - to give you a complete weed control program.  Something to think about.........