not sure but you have to be careful when treating st. augustine or centipede since they are really weeds themselves and not grass. many weed killers will also kill those types of grasses or damage them. sometimes you can still use them but you just have to mix it up watered down a bit more. sometimes it can turn the grass a yellow color when using it on these types of grasses.
usually with centipede or st. augustine you don't have to worry about weeds though as they will eventually choke them out. you might could just fertilize the grass and see if that works.