If you want to keep the St Augustine, it should never be cut below 3". A sharpened lawn mower blade would be a good idea as well. I had a look at that fertilizer. That explains the green bermuda and yellow St Augustine.
They who can give up essential liberty to obtain a little temporary safety, deserve neither liberty nor safety.
Benjamin Franklin 1775
Sell not virtue to purchase wealth, nor Liberty to purchase power.
Benjamin Franklin Poor Richard's Almanac1738