Fall is the best time to get a great kill...that is when fescue is storing nutrients into the root system. I had great luck this year in November before gun season and that fescue is already turning brown so it will be an afterthought next spring. Basically if it is still green and you have 3-4 more warm days left, I don't see why you would not get a kill, especially for southern MO. I would hesitate for up in my area though by the IA line to spray this time of year. :cheers:
Spring is the next best time to get a great kill and like Sully stated, early May would be a sure bet. On years where it really starts to take off sooner from hot springs, I would start spraying before that tho.