I am growing a 3 acre parent sunflower seed block on the edge of a corn field.  The company rep now wants me to spray it with Express herbicide for chemical rogueing since it is a tolerant variety.  They failed to inform me of this requirement at planting.  It is planted in a corn field with another corn field adjacent.  Question is, will it hurt the corn to get overspray and drift since I will have 30 inch buffer on one edge and about 50 feet on the other?