Does not harm grass but does little harm to weeds as well. Can't be used on irrigated lawns or when rain expected for 2 days ( remember Augustine grass is in daily shower prone areas). Can't be used if temperature too high ( remember Augustine grass is hot weather lawn !!) Sprayer must have perfectly calibrated spray nozzle according to instructions ( yeah, right, how do you do that???).
I'll give it some more time to work but won't buy again.
I had been buying Image brand atrazine at Home Depot for years, but they stopped selling it so I bought this instead. Even though I followed the directions exactly, it didn't seem to work nearly as well: not as many weeds were killed and those that were took much longer than with the Image brand.