The only thing I know that kills po-anna is Image. And it is expensive and iffy. It may also damage your fescue. I have bermuda and Image doesn't hurt it, but I used a lot last year to get rid of po-anna and it was iffy at best.

A pre-emergent such as Halts used in the fall is supposed to prevent po-anna, but I found that to be iffy too.

This year we hired chem lawn. Even paying them to come is cheaper than buying the stuff ourselves and we have much better results. Whatever they sprayed on our lawn killed the oxalis we were inundated with and took care of most of the poanna.

Since you have fescue, I'm assuming you have a lot of shade. Unfortunately poanna survives better in shade, I don't have any in the sunny parts of my lawn, but it thrives in the shady spots.

Good luck!

Yes, you can definitely put pre-emergent down now and it will not hurt the fall fescue seeding. However, do consider that you have to put pre-emergent down BEFORE weed seeds like POA germinate. Unfortunately I found this statement on a Perdue.edu website about golf course maintenance dated in September:

Poa annua germination peaks in September and October, but will continue to germinate throughout a warm winter and well into spring. Open turf from late aerification will encourage Poa annua germination. Additionally, bringing soil cores to the surface will also bring viable Poa seeds to the surface further encouraging germination. The best method to help limit Poa encroachment at this time of the year is with preemergence herbicides. A number of products are labeled for Poa annua control and applications around Labor Day are most effective. However, if no preemergence herbicide was applied yet and aerification is still scheduled for this year, itÂs not too late to apply. A benefit of applying preemergence now is that it will continue to limit Poa germination throughout the winter and spring and will prevent summer annuals like crabgrass from germinating early next summer.

So it sounds like POA is germinating about the same time you want your fescue to germinate. Putting down pre-emergent now may not help you.

You might be able to find more information if you google "poa annua germination" or "poa annua control" and look for links to southern sites. Here is a UGA site.

Here is a link that might be useful: UGA poa annua

I can't remember what I wrote in the lawncare forum but I have a section of my yard that is Kentucky Bluegrass and I used image (which is for warm season grasses like bermuda) to carefully spot treat and I was able to get good results without noticable damage to the bluegrass. You might try that to spot treat in a pump spray on a day that isn't windy.