My boys and I spend about a week every spring cutting, bagging and burning those devil weeds around our farm! If you mow them once they head out like that they will still dry down and fluff seed. You must get rid of them completely, then remember to get after them EARLY next spring with chemicals before they are mature enough to head out. You stirred up some dormant seed when working your plot and it will only get worse if you don't get after them right away. Damn I hate those vile things!!!