Have a dozer handy and be prepared for the worst. Know the wind speed and direction, and backfire it. Put out any areas that junmp your line quickly. Have alot of help with the right tools on hand.
I dont know how overgrown the field is, or how large it is, but they can get out of control really quickly, especially if there is any wind. I would rather burn a woodlot any day.
Burning is a great way to get rid of fescue, and get a field manageable in short time, but make sure the conditions are right before you light it. I have seen people start a field and have flames 15 feet high before they finished lighting it. If you do it right, you can creep the fire across the field and get a good burn without the hazards of huge flames and blowing embers. If you do it wrong, you will know pretty quickly.