Cut your pasture fairly short then hose it this spring with roundup after the weeds turn green but before the bermuda sprigs. Roundup wont kill bermuda while its dormant but itll kill the bushes dead enough to dig up a root ball.
If you weren't so far away I would come down and mow your field. I had a hillside which was covered in rasberries 6' tall and barberry an invasive prikley bush which is the worst stuff of all. I mow twice a year and the stuff has learned to go someplace else. Stay away from the pesticides they just aren't good for the environment.