I've personally never had success using Celsius WG in St Augustine grass to control crabgrass. I know it is labeled, but I've never had it work.

I use SurePyc IQ; be careful, because it can be a hot mix, but it has melted the crabgrass and tropical signalgrass our of zoysia and St Augustine for us.

 

Thanks!

 

It's really late in the season and you are fighting crabgrass when it at full strength. remember that it die on it's own first freeze.

I have STA and use very little post emergent herbicides on it. I can't remember using anything other than MSM turf and sulfentrazone ( I making my own Blindside) I mix with my pre m.

if doing just your own yard with STA, you may want to use atrazine in the spring with your pre m.

My tip is start with a pre emergent this fall, again next spring. Work on the over all health of your lawn, mow it at 4 inches or so, and out will shade out most weeds.

I mix MSM turf with the pre m because it does give some reach back on crabgrass. Crabgrass used to be on the label for control in Centipede, but I guess it wasn't effective enough. It's still able to kill very young crabgrass that may have germinated before you spray your pre m. Atrazine will also kill very young crabgrass.

When using any herbicide on STA, you generally better off doing it in the early spring.

 

It could be your application timing. Per the label its best controlled at early stages of growth with multiple applications.

 

Yes, it's been my experience that it's very hard to control in August, even with quinclorac, which can't be used on STA. You just going to spend a bunch of money and ding up your turf for something that would have died soon on it's own after you finally kill it.