Two products we carry that have an active ingredient closest to MSMA are Quali Pro MSM 25 OD Liquid Herbicide and AmTide MSM 60 DF Herbicide. St. Augustine grass is labeled as a tolerant to both of these products though, as well as Emeral Zoysia. Your best option though, will be to spot treat with Roundup. St. Augustine and Zoysia are closely related so whatever is safe for Zoysia will likely be safe for St. Augustine as well.
Yes, Quali Pro MSM 25 OD Liquid Herbicide can be used in a hose end sprayer. The rate will depend on the type of turfgrass you are applying the product to. Please consult the product label to find the correct rate for your needs.
Per the label of Quali Pro MSM 25 OD Liquid Herbicide, you need to use 1.12 to 2.23 oz per acre to kill dollarweed. That means you would use 0.026 to 0.05 oz per 1,000 sq ft. Water is just the carrier, to decide how much water you need to use, you should mark a 1,000 sq ft area, fill your sprayer with water ONLY, and start walking and spraying just as if you were doing the actual application of herbicide. When you are done walking and spraying the 1,000 sq ft area, note how much water it took you to spray that area. That is the amount you will want to mix the product with for each 1,000 sq ft area that needs to be treated. We recommend not treating your lawn if it's still dormant or coming out of dormancy.
Quali Pro MSM 25 OD Liquid Herbicide is not labeled to treat for sandburs. You could use a product like Image Kills Nutsedge Concentrate instead. It is labeled for sandbur and would be safe to apply to St. Augustine grass as well.
Quali Pro MSM 25 OD Liquid Herbicide has a three year from date of purchase shelf life if stored in cool, dry place away from extreme temperatures. If mixed with water, you should apply the finished solution within 24 hours of mixing.
Quali Pro MSM 25 OD Liquid Herbicide can be applied to established St. Augustine and will injure bahia. A repeat application may be needed in 4-6 weeks from initial application. It is applied at a rate of 0.56 to 1.67 fl oz per acre for bahia.