Question
how do you get rid of kikuyu and st augustine grass from infesting a marathon lawn.  this is is pasadena california.  what chemicals do you use or is there a natural way to do it?

Answer
The only approach I could recommend is using Roundup. Kikuya is brutally resilient and will not die easily. It also spreads like a fire on a lake of gasoline.

Unfortunately, this is a bit of a "start over" where you'll just need to kill it all off, dig out the dead stuff, spread some new soil, and replant.

Sorry to be the bearer of bad news.

-C.J. Brown
www.TheLawnCoach.com