What kind of grass? High rates of metsulfuron methyl are a no no on centipede or zoysia. On bermuda, it is not so bad, however why yellow a lawn if you do not have to. I can only guess that they did it through a hard to calibrate sprinkler nozzle rather than a boom. Reason why I would stick to the lower rates of both is that iodosulfuron(Celsius) breaks down to metsulfuron. Essentially applying a double dose. I have never applied more than 1/2 oz per acre metsulfuron unless spraying brush in non crop areas.