I'm looking on an I-phone screen but agree with others that this looks like JG. There are lots of good ID links that you can Google since it is such an invasive species.
Tip: After you kill the plant, mark that area of the field some way and check it each year about this time for more that have sprouted. This isn't likely the first year that plant has been there and could have dropped seed in the past. Like many other plants, the seed don't all germinate the same year, so you could get new plants emerging for quite some time.
Best wishes.