Bermuda grass and Nut Sedge are incredibly difficult to eliminate by any means other then using chemicals.
There is a lot of argument over whether a 20% vinegar spray will knock out the Bermuda grass in the organic forums.
- The consensus is once you have bermuda grass it is incredibly difficult to eliminate due to its root structure and stolons.
- Here is a sample thread.
Every organic landscape professional I know agrees that Nut grass can only be wiped out chemically.
- There are a number of nut sedge specific chemicals available and do use these NOT Roundup which will not get rid of nut grass.
- Alternately you can attempt to remove the nut grass and its "nuts" by excavating all the soil for a six inch depth and width around the grass and dispose of the soil "elsewhere" while hoping you got all the nuts.
- See this LA Times article for more on this solution and a chemical solution.