This is vernonia altissima. The common name is Tall Ironweed - and it's called ironweed for a reason. The stalks are tough and the roots tougher. It's almost impossible to pull out even in wet boggy ground.
Horses won't eat it. Cows won't eat it. That's why we have such beautiful fields full of it - the animals eat around it, limiting the competition, then it blooms and each cluster has dozens of blooms and each bloom has dozens of seeds. It self sows readily and pretty soon there are fields full.
Personally, I think it's gorgeous. You can't beat that color and it lasts for weeks and weeks.
It's hard to photograph in fields because the colors go brown, but I'll keep trying and post here if I get a good one.