Japanese Knotweed

Q: My neighbour and I have both got japanese knotweed in our gardens.  We have both used Roundup tree stump and root killer.  The knotweed although rather a large clump has died right back and just black dead looking stumps and other dead stems remain.  What should I do now, remove the stump?  Your advice would be very helpful.  Regards, Lynne

A: You would be best now to try and remove the dead stuff including the stumps, however, you will be very lucky if you have eradicated the knotweed as it is very persistant.  Be ready with the Roundup that you used before.  It often takes up to three years to completely eradicate.