Hello!

Controlling poa annua is very difficult and it will take consistant effort over time.  But it can be done! The September application must be applied and watered in by September 1st in NC.  Hand pulling when possible will also help and you may want to rotate herbicides to avoid herbicide resistance.
 
Note that the downside to these herbicides uses will prevent any reseeding of tall fescue and other cool-season grasses. The most effective strategy is to utilize cultural practices (including seeding) in fall that maximize turf growth and minimizes sunlight penetrating through the canopy. Soil shading is the best defense against poa annua.  Also, do not use high nitrogen fertilizer during poa annua peak germination periods.  This encourages poa annua spread and survival into winter and spring.

I have a table below from the University of Georgia Extension that list herbicides and which is most efficacious and which to use during as a preemergent, (September) or postemergent, (Spring).

 Here is the link for specific details that may help as well.
https://extension.uga.edu/publications/detail.html?number=B1394&title=annual-bluegrass-control-in-residential-turfgrass

Efficacy of preemergence herbicides for annual bluegrass control in residential turfgrasses

I 

Table 2. Efficacy of preemergence herbicides for annual bluegrass control in residential turfgrasses.
Preemergence Herbicides
atrazine	E
benefin	E
bensulide	F
dithiopyr	F-G
ethofumesate	G-E
oryzalin	G
pendimethalin	G
prodiamine	G-E
simazine	E
E = Excellent (90 to 100%), G = Good (80 to 89%), F = Fair (70 to 79%), P = Poor (<70%). Efficacy of postemergence herbicides for annual bluegrass control in turfgrass. Efficacy of postemergence herbicides for annual bluegrass control in turfgrass. Postemergence Herbicides atrazine E foramsulfuron E glufosinate E glyphosate E imazaquin P-F simazine E sulfosulfuron P-F trifloxysulfuron E E = Excellent (90 to 100%), G = Good (80 to 89%), F = Fair (70 to 79%), P = Poor (<70%). I hope this helps!  Please let me know if you have any other questions.   Good luck!