Blackberry (Rubus species)
Wild blackberry can be a vexing weed almost anywhere in the United States, but it's particularly troublesome in the Northeast,
the Southeast, and many areas of the West. Plants spread rapidly by underground runners and by seed.
Pull young plants in spring, before they develop a perennial root system. To kill established clumps, repeatedly prune back the stems as they sprout; this eventually exhausts the roots. Or mow the tops and dig out the roots; repeat the process as new canes grow from roots left behind.
You can also cut stems to the ground and apply glyphosate to the stubs as soon as possible after cutting. Spot-treat any new shoots with glyphosate as they appear.