I would further suggest you click back into your profile and redo your location. Texas is waaaaaaay to big to give any meaningful answers. If you live in Dalhart then you have no business trying St Augustine. And if you live in Dallas, pleeeeze don't say North Texas. Be specific. Other terms that don't fly are West Texas, Panhandle, Central Texas, Hill Country. South Texas, Rio Grande Valley, etc. Name the town or community nearest to you.
Okay now I'll try to be helpful. Stop throwing stuff on the lawn. Stop altogether. Relax. At this point you are doing more harm than good. Three applications of herbicide already is way overthinking it. Here is how you get great St Augustine in order of importance.
Watering
Water deeply and infrequently. Deep means 1 inch all at one time and not spread out 1/7" per day. You can set out cat food or tuna cans and time how long it takes your sprinkler(s) to fill all the cans. That will become your new watering time from now on. With my water pressure and oscillator sprinkler/hose combination, my time is 8 hours. Some high flow in-ground systems can deliver 1 inch in 20 minutes. Your time will likely be in between. Frequency depends mostly on the daytime high temperature, but once every week or two is about right this time of year. If your temps are in the 80s, deep water every 2 weeks. If your temps are in the 90s, then weekly should be good. The delayed watering helps keep weeds away, because weed seeds need daily watering to germinate. If you have been watering more often than once a week, that would explain your need for so much weed control.
Mowing
Mulch mow every week or two at the mower's HIGHEST setting. There is never any reason to mow St Augustine at a different setting. The tall setting prevents weeds and slows down evaporation from the soil.
Fertilizer
Apply your FIRST dose of nitrogen fertilizer in May (now). Oops, too late for that. When St Augustine awakens it already has all the nutrients it needs to go into May, so adding more only works against you. You'll still have to apply more in May. Apply a second dose of chemical fertilizer in October when the summer heat starts cooling off. Apply the last dose in late November. However, if you want to use organic fertilizers, which just about everyone on this forum would encourage, then you can do that now without worrying about the early fertilizer effect. Organic fertilizer works differently and can be applied any day, or every day, of the year even if you just applied chemical fertilizer today.
That's it. Note that I did not mention herbicide. Herbicide really falls off the list of things to do if you are watering, mowing, and fertilizing as above. If you want to use one, this stuff works like magic for almost all the weeds. If even kills poa annua permanently.
You only apply it one time in mid April, again, too late, and it is pretty good for the long term future.
I also did not mention insecticide or fungicide. If you think you have an insect or disease problem, please write back with particulars and pictures.
