I apologize for this delayed reply to your gardening question and hope it is still helpful to you.
That will most likely work although some St. Augustine may survive and grow through here and there. I suggest an easier approach. Spray the existing St. Augustine with glyphosate (Roundup is one brand) and then wait for a week for it to completely kill the turf and any weeds. Then rototill lightly and seed the area with Bermuda grass. Water then seed in well and keep the soil moist until the Bermuda plants are up and growing well. I suggest you use a semi dwarf type of Bermuda grass such as the variety 'Sahara'.
Thanks for the question. Best wishes for a wonderful gardening season. Please stop in again soon!
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