Holy Crap !!!!
Don't let that thing go to seed. In a couple of years, you'll be hip deep in them. They can take over a pasture VERY quickly. I go out into our pasture every 3 days or so and chop them this time of year. Musk Thistle and Bull Thistles are a noxious weed in Kansas and you can be fined by the county. If the flowers are showing purple and you chop it down, the flowers will continue to grow and go to seed. You have to pick the flowers and chop it below the soil level to kill it. If my garden would only grow as well. I have spent HOURS trying to get rid of them, but if your neighbor to the south doesn't kill his, you'll be back cutting them next year. (prevailing wind is from the south in summer).
Being in Kansas, you probably already know this.
I lived in JA county back in the 80's...had a place on the res.