Can't tell a whole lot from your photos, but take a look at
descriptions of "Japanese knotweed" -- may have the scientific
names of Polygonum cuspidatum, Renoutria japonica or Fallopia japonica.

If that's what you've got, you're in for a battle, but do keep after it.
It only gets worse.

http://plants.usda.gov/cgi_bin/plant...?earl=plant_pr
ofile.cgi&symbol=POCU6 (paste the URL back together)

http://www.nps.gov/plants/alien/fact/pocu1.htm
http://tncweeds.ucdavis.edu/esadocs/polycusp.html