Things not dying is a clue. I am aware of the nuances involved in public area weed control. Johnson grass hit with Arsenal or Velpar does not grow back. I have what is called Napier grass and itch grass in Hawaii. Those grasses are inherently resistant to glyphosate. A treatment with glyphosate normally partially kills it only to have it grow back from the clump. 1 qt per acre of Arsenal kills it and keeps it dead.