I didn't think 2,4-D would kill ANY kind of grass...I thought it was a broadleaf herbicide.
Before you buy anything, check with your county ag office. Around here, the county will give you 2,4-D for free if you are using it on noxious weeds (thistles, etc.).
The local paper had an article about how fescue is harmful to wildlife.
edit: I can't remember if it was 2,4-D or 2,4,5-T that we had sprayed out of a Cessan Agwagon. At any rate, it had to be flushed out because the next load was insecticide going on a row crop. There was apparently a little bit of that stuff left in the lines and we ran a tank of water through it as it sat on the ramp. When we came to work the next day, the area around the plane was littered with thousands (well, hundreds anyway) of little dead frogs. Something about that stuff attracted them from far and wide and killed them; there were so many we swept them up with push brooms.