How can I kill Kikuyu in my Winter Green Couch without killing the Winter Green Couch

There is a commercial grade selective herbicide available that controls kikuyu in couch lawns but there isn't one for the home garden. You can Google ideas from Greenharvest. Alternatively, you can hand remove the kikuyu or very carefully brush it with glyphosate taking extreme care not to allow any of the liquid to drift on the surrounding couch.