FYI, last year when we were killing milo prior to harvest we were adding 4 oz SuperB (Winfield petroleum based crop oil).  I left it out on the last load so I wouldn't have to clean the sprayer for the next load which  was gonna be cotton.  I didn't kill the milo, almost looked like I left the RU out.  Also, if you have aphids on the Johnson grass, it will be hard, if not impossible, to get it to adsorb into the plant.