St Augustine grass
Thank you for the question. Have you taken a soil sample and had the soil tested for Phosphorus, Potassium and pH? If you have, I would recommend following the recommendations for fertilizer on the soil test results.
In the absence of a soil test report, I would recommend any of the turf type fertilizers. Those fertilizers usually say for lawns on the package and have a ratio of 4:1:2 or 3:1:2. 16-4-8 and 24-6-12 are two very common turf type fertilizer analysis.
I don't usually recommend a weed and feed, because most often people want to control weeds now and the lawn doesn't need to be fertilized until May or June.
As for weed control in the lawn if you prefer to use a granular weed control product look for one that is light weight. Most granular products will have on the package that the granule needs to stick to the leaf of the weed in order to control the weed. This usually means the leaf needs to be wet when the product is distributed. Liquid products will stick to leaves of weeds much easier and even better if a surfactant or spreader-sticker is mixed with the product. Again follow the label when mixing something with the product.
Many of the liquid products say on the label not to apply during spring green up, which is happening now. If you do decide to use a weed control product, make sure to read the label and make sure it is safe to use during spring green-up. It would be a good idea to read the label of any granular weed control product to be sure it is safe to use during spring green-up as well. Many of them have the same active ingredients and could damage the grass if applied at the wrong time of year.
If I knew what weed you are trying to control in the St. Augustine grass, I could be more specific as to the active ingredient to look for when selecting a product for best control. I do hope this has provided at least a little help.