My husband and I live in Palm City, FL (south Florida), and have St. Augustine grass in our backyard. It's a year old, it was put in when we had our house built last year. We fertilize it as recommended and it is always nice and green. We just did our fertilizing 2 weeks ago, and the front half of our backyard is green, thick and beautiful but the back half is completely dead!!! Does anyone know why this is? Did we over-fertilize? Or not fertilize enough? We thought we spread it evenly...

Any help is appreciated on how we can get our grass fixed. :-) Thanks in advance!

I have attached a picture of our entire backyard. The dead grass is in the back (along with a closeup of the dead grass) and the healthy grass is in the front. It hasn't been cut in a while, so don't mind that it looks so uneven...