Weed control for St Augustine grass in Austin, TX

Sorry for the spam! Thought that this is right forum to ask as we have lot of lawn enthusiasts here.

We have 3500 sq ft of lawn with St. Augustine grass located in Austin, TX area (Zip code 78681). It was bad last year with our lawn with fungus, stressed out areas. Almost 50% of it was dead. I installed Rachio in September of last year. Now lawn came back to life. It is luscious green. But I have areas where I see lot annual blue grass and little bit of crab grass. I read spraying a pre-emergent herbicide is the way to go to treat them effectively.
I am looking for suggestions for herbicides and what time of the year do I need to spray them.

I appreciate your help.

Contact the Travis County Extension Service or Texas A&M turf website. Good luck with St. Augustine in Austin. It’s not a good fit except in shady locations.