04/05/2012 at 12:44
Sorry hit the wrong button!
In my experience digging it out while it is still alive is a decidedly bad idea as one seventh of a gram of root can result in re-growth.
Having spent wasted time trying to spray the stuff we came up with a more radical approach.In Spring, wait until it have reached at least 75cm high, it needs to be making strong growth.Cut the top off so that you can see down the stem, which is a bit Bamboo like in that it grows in section. Straighten a metal coathanger, and poke this down through the sections as far as you can. Make up a solution of Glyphosate, from the concentrate, then using a hypodermic syringe or similar (you don't need a needle) inject the solution carefully into the stem and keep doing this until the stem is almost full. Then proceed to the next plant. Repeat this in Autumn, when the sap is retreating into the roots and again the following Spring, by which time the plant will really be struggling. Once you are certain it is dead and you may need to wait a further season, then it is safe to dig up and dispose of legally.
We have used this successfully on Knotweed which was over 1.8m high and it didn't endanger any of the surrounding trees or shrubs.