Clethodim & crop oil is now your post emergent. Still avoid spraying on tree even though it's theoretically no issue. Mix it with any combo of these PRE-EMERGENTS (and yes, I can tell you how much of each if needed)... I'd pick 3 of these, ideally 4. 3 will cover the nasty grasses, horrible weeds like Pigweed & Waterhelp, lambsquarter, ragweed, etc, etc.....
-Surflan
-Atrazine (simizine if unable)
-PROWL H2O (do this! also color is orange so you know where you sprayed)
-S-Metolachlor or Acetochlor - can buy anywhere, called stuff like "DUAL II MAGNUM", Warrant, Brawl I think?, etc, etc. Common.
-Plateau/Panoramic/Journey, all the same. Low rate stuff so it's not really expensive when you figure it out. and it works incredibly well, insane good.
All of em are good and if you really wanted to, could do all of em. "BUT DUDE, THAT'S A LOT" - no, not really, it's not that bad, you'll use it if you buy in 1 or 2.5 gallon containers (even next year, whatever). You don't wanna spray just one thing where it won't cover "XYZ weed" and you're screwed. Trust me, do it right. This stuff is not hard to find, anyone can order, spend the money and do it right. Anyone who cheaps out on the herbicides, it's one of the MAIN reasons I see thousands of dollars of tree plantings and days of work completely go to waste. Do the spraying right!!!! Good luck!!!