Rimsulfuron 25DF is not labeled to be used on St Augustine grass specifically, only warm-season turf such as Bermudagrass, zoysia, and centipede. We would not recommend using this product on St Augustine grass. You could test a small area first for tolerance, but we cannot guarantee that it would not damage the turf. Keep in mind that this product is not for use on residential turfgrass. If you would like to tell us what weeds you are targeting, then we can recommend an alternate product for you.
Certainty Herbicide is a great option for a warm season turf like Bermuda to remove poa annua and other broadleaf weeds. We would recommend putting down a split application of a pre emergent like Pendulum 2G this fall to help prevent the poa annua from coming up next spring. To learn about split applications and why they are beneficial you can see our How To Video Here.
We recommend contacting the manufacturer of Rimsulfuron 25DF Quali-Pro directly with specific product questions by calling 800-242-5562, or via their website's contact page here.
