This plant is called purpletop vervain. It is one of the most heavily browsed species on my property. All of what I have has come back from the natural seedbank..... but if you don’t have this plant present in your summer fields then I think it would be well worth getting it started in the mix. It should reseed itself from there. I’m going to see if I can collect some seed from this powerline to put out in my big field. It’s pretty scant in the big field.

https://www.google.com/?gws_rd=ssl#q=purpletop+vervain+seed&tbm=shop