Dig it out - its not an easy task, but not impossible either. Last one I did took me about 2 hours as I recall... and it was a very large one. Burning won't kill it anyway, it responds to being burnt by growing rapidly if there's any life left in the roots.

" Last one I did took me about 2 hours as I recall"

You've more patience tham me Bamboo. I gave up after 30 minuters!.

Large pampas are absolute devils tpo dig up!

Lol, even worse than the pampas was the thick vinyl pond liner I discovered 2 feet beneath it and stretching 4 feet either side of where the pampas had been...