I apologize for this delayed reply to your gardening question and hope it is still helpful to you.
To my knowledge there is a way to kill carpet grass but not St. Augustine grass other than ether and pulling/digging the carpet grass out or spraying and killing everything and then replanting St. Augustine. You might try contacting County extension office to see if they are aware of any other options.
Thanks for the question. Best wishes for a wonderful gardening season. Please stop in again soon!
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