I would never walk an edge of a tree line without being in the corn. While they like bedding in the corn... they love bedding and milling right along the tree's edge that borders a standing corn field. It would be suicide to walk inside a tree edge to get to a spot even for a PM hunt.
Might be suicide in ND, but here in Virginia its common sense. Most corn fields here are surronded by mature hardwoods, or loblolly pines. Since the corn isn't planted butt up against the woods, there's normall a 15-30 foot boarder of just grass. You can walk it as quietly and stealtly as can be, without being in the woods, or the corn.