Oh dear
> One of our sites has had Japanese Knotweed identified on it. We have
> contacted DEFRA, The Environment Agency, The Local Authority and English
> Heritage but nobody seems to know how to deal with the problem and
> not from an archaeological perspective. It is in an archaeologically
> sensitive area and an area scheduled for development in the very near
> future. It is my understanding the only way to deal with the Knotweed is
> dig a very big hole and indeed would be an offence under the 1981
> Countryside act not to.
I've been battling this beast for most of my professional career as a
landscape architect - and still am in a current project. It can regrow from
a piece of root weighing as little as about 0.7g. Strimming it is a disaster
as all it does is spread pieces about the place which root and grow. Its
roots can go 2m deep and spread 7m laterally in a single year!  This weed
can be controlled with a glyphosate herbicide, but it will take about 3
years at least to get rid of it. The best time to spray it is in autumn when
it is withdrawing resources from its leaves and shoots to its roots. The
National Trust used a technique in Cot Valley near St Just in Cornwall which
was very successful, but it's not a legally approved technique and would
need special permission. The way this is done - only with the right approval
of course - is to cut the shoots off, pierce the membranes down inside the
hollow stem with a spike and then inject glyphosate directly into the stem
using a drench. I should point out that I don't have the necessary
registration to advise on herbicides so please check all this elsewhere :o)

It can be contained by covering it with an extremely puncture resistant
geotextile - the sort used under ballast on railway tracks works. The
problem with this is that the roots may simply go dormant and regrow as and
when the ground is disturbed again. It can in theory be excavated and
disposed of in a properly licensed landfill site, but this hugely expensive
and most landfill operators wont want it. It can also be excavated and
spread on another part of the site for treatment with herbicide however this
needs doing with extreme care to avoid simply spreading it further.

I'm always willing to help get rid of this stuff!

Cheers - from Knotweed infested Cornwall