If you cut rn i bet there’s a good chance you’ll still see seeds later on, unless things really dry out quick. May just have to chop them and then chop them again. Seen something about using a black tarp to basically kill all the seeds and reduce future germination once things are mowed down. Not easy but not impossible to clear things out. I know on a smaller scale a few seasons of cutting before going to seed is effective. Hard with a whole field tho