It *might* not be a TOTAL disaster - just a Very Big Problem.  I spent a ton of time online last night (instead of doing laundry,) and it appears that we may have dwarf knotweed instead of full-bore Japanese Knotweed.  It's still horrifically invasive, but not to the "mutant killer weed from Mars" extent of it's big cousin.  Time and weather permitting, I'll go back and inspect the enormous mound of detritus and see if I can see any sprouts.  If so, this weekend I'll plan to dig out that area with extreme prejudice and figure out how to burn what I've dug.  I'm not really sure how I can do that without setting either the house or the woods on fire.  We don't have much clear land.  Minimally, I'll tarp/bag it in the sun while I figure it out. 

I've found a bunch of websites from the UK and the US detailing various control strategies - organic, chemical, and large scale.  I should be able to take enough information from those to deal with this.

Here's the really awful part - I think this stuff was planted intentionally!  There are a few varieties of polygonum that are non-invasive, but this one is downright thuggish, and it's still sold as groundcover.  People are stupid.

Now I'm afraid to dispose of *anything* I have to dig up...