I would spray first, and then cultivate.  Most definitely.  

Most residual herbicides in my opinion will benefit from the cultivation.  I doubt you'll be cultivating too deep for the cultivation to be a detriment to the residual herbicides.  The cultivation will help provide some benefits for the corn.  Definitely, in my opinion.   Roots need some oxygen.  Cultivating will help with that.  Plus, it wouldn't surprise me that the corn will come close to canopying soon enough after the cultivation to thwart any unwanted new weed and grass emergence.




gordon