Last year we used valor and callisto 2 to 3 weeks before planting. Then when corn was about 5" tall sprayed callisto, outlook, atrazine, and roundup. Only one field had grass in it that was not johnson grass. Most fields have at least some johnsongrass which is why roundup was in the mix.  Worked really well and plan to do very similar this year, might switch the outlook out for zidua since it is better on pigweed and the price is becoming more competitive. 

The fields that had really bad grass 11 years ago have received 6 to 9 ton of lime during that time as well.