Can it rescue you from a crappy situation?  Probably.  But.... you can play a little fast and loose with corn chemistry, there's lots of product and timing options to whack broadleaf weeds there.  More than once, I've been folding the planter at 2 or 3 am while the sprayer is unfolding to follow me with bean pre when we are up against the weather.   There's just nothing you can do post that is less expensive or more effective than laying down a solid base.  And yeah, spraying in the middle of the night isn't gonna be easy if you are hiring it done.  Sure has saved our bacon a few times though.