Here at the farm, I use roundup concentrate, diluted with water per instructions in a backpack type sprayer that I mount on my ATV. Ditches and edges. Twice a year. Works fine.
My 3 gal jug of concentrate has lasted 3 years and is still half full. So not using a ton of it. But works well for the limited amount I use. I only use on dead calm days because the overspray takes out anything near it!
Years ago when I was a kid, we used 2-4-d but didn’t think you could get that any more. That was in a big thre point hitch boom sprayer. Used to kill off pastures that had a lot of crap and milkweed before disking and planting in clover and grass for hay. But that was my old man, not me. So my memory may be off. But I think the jugs said 2-4-d Amine? If that rings a bell. Again, I thought that stuff as banned long ago. But sounds like not? I was told to “get lost” when he was spraying, so assumed it was nasty. That was 45 years ago! I don’t do much weed killing now!
Sirhr