Cut them to the ground, drill holes into the stumps (don't break through the sides), and then pour concentrated RoundUp into the holes. Or just spray the shrubs themselves.
Elbow Grease and a shovel is the best way to rid the garden of of almost anything. There are so many harmfull products on the market that affect our health and enviroment. Getting back to the basic's guarentee's the User a 100% success rate.