Answer: Japanese knotweed is a terribly invasive plant. It can sometimes be dug out however any shred of root left behind will result in regrowth. You may be able to control it with careful applications of herbicide containing glyphosate or triclopyr. Here is additional information on how to apply it to either the cut stems or the foliage.
You may need to cut and paste the complete url into your browser to make it work correctly. Also, your local county extension may have recommendations for you. Best of luck, I know this is a big job.
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