A good brush killer is Tordon. You can get it at a Farm and Home type store. Home Depot and Lowes won't have it. All you have to do is break a couple stems, spray the stems and the plant dies. Just wear gloves and follow directions because it is potent but works great for weedy wood stemmed plants. We use it on bush honeysuckle that every now and then will pop up. We killed most but a few still come back every once in awhile.