One problem is the seeds, I've read they can be dormant for 4 years so, dligent use of premergent is required even if you manage to kill the plants with post-emergeent. I think Dithiopyr (Dimension) may be a little better than other pre-ems. OR, use Dimension in spring and a different one in fall? Curiously, I have read that chickens will eat the seeds !!!
At present, my go-to formula for spot treatment in my lawn is 4 oz of
Bonide (BND069) - Sedge Ender Weed Control Concentrate, plus, 2oz of
Image 100099405 Kills Nutsedge Concentrate in a 1 gal pump. It has helped me a LOT with most standard problems (spurge and dandelions, etc.) as well as Crab grass and even sandspurs and asiatic dayflower. It can stress St. Augustine but I seem to have avoided that problem.
I now seem to have a very stiff, low/creeping, mat-forming woody weed in a few spots. small, linear leaves on green branching stems, the leaves are alternate. I noticed it recently when I mowed a little lower than normal - it is 'under' the St. Augustine. It grows sideways! Dunno what flowers or seeds look like. I don't have a lot of it, just can't ID it. Kinda like a Knotweed but the leaves are VERY skinny.