I've had a go at killing japanese knotweed using the National Trust
approved technique of cutting and injecting glyphosate into the
cut stems, followed by burning the cut material on site.

http://www.nationaltrust.org.uk/main...vironment/w-na
ture/w-nature-projects/w-nature-projects-japanese_knotweed.htm

Its too early to say whether its worked. I'm sure there will be
some mopping up to do next spring and anyway, we're supposed to
watch the site for three years.

It occurred to me that it might be possible to do the same
with mares-tail (Equisetum Arvense). If you cut the stems
it should be possible to dribble liquid in which would go down to the
root. It would be slower work than spraying but would have the
advantage of being far more accurately targeted. I did a web search
and found that Monsanto already suggest you can do this
http://www.monsanto.com/ito/pdfs/Rou...rateHollow.pdf

Has anyone tried this? It doesn't seem much more labourious than
the suggestion to bruise the stems, then spray.