Answer: I think you are describing Polygonum cuspidatum, or knotweed. It is truly a horror and is able to regenerate from even small broken bits of stem or root. So tilling and simple pulling will not work. Studies seem to indicate it can be controlled by repeated cutting combined with an August application of glyphosate (the active ingredient in Roundup), or possibly cutting and covering with black plastic to exclude light -- although with the smothering in my experience it will come back later if you try to plant the area. I would suggest you work with your county extension to get a specific identification of the plant and based on knowing that, their control recommendations. It is considered a serious invasive exotic weed and so they may have some additional control suggestions. Good luck!
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