I was chatting to a mate who works for the Council Parks Dept the other day and the subject of Japanese Knotweed came up.
He reckons they have found the best way of killing it, is to either snip a hole in the stem or cut the plant off about 12" from the ground, and fill the hollow stem with glyphosate. Will need to be repeated a couple of times but apparently this is very successful.
Young knotweed can be sprayed as soon as it appears.
Hope this helps.
Every bit killed helps... a regular nightmare... :o
I cleared it with glyphosate, even where growing into a hedge, just sprayed it every 4 weeks during the Spring and Summer and it failed to appear the next year.
I did not cut it down but kept on spraying the same stalks on which new leaves would appear, and any new shoots as they came up.
It can also be eaten.
http://www.wildmanstevebrill.com/Web%20Recipes/Recipes%20Page.html#Anchor-Japanese-47857
Pouring glyphosate in about September works well, as at that time the plant's taking goodness from the topgrowth down into the roots, and it permeates everywhere. It needs to be repeated in subsequent years to kill off the last bits.
This concentrated stuff claims to get rid of it. It works out a lot cheaper than usual, I think the bottle makes about 25 litres at standard strength.
http://www.wyevale.co.uk/Scotts-roundup-tree-stump-killer-+250ml/0800002311,default,pd.html
and Lewic, that stuff also works well on Horsetail - without the need to bash and bruise each stem first.
We have a really bad Knotweed problem on our site - the contractor who manages the sites for the Council is showing some interest in tackling it, but subject to funding ::)
Got it up our allotments, I just kept pulling the plants up, the roots didn't seem to go down too deep. I sprayed the neighbouring allotments with Weedol, that seemed to do the trick, although some just wilted over and continued growing at a wierd angle... oh well. :P
We've got several stands on our site, where it was allegedly introduced, and certainly spread, by a former committee member. It's all over three of the plots she had, and in a few other places down the stream. The Council's doing a great job getting rid of it.
Had it in my garden from the pub car park next door. It eventually pushed the wall over and the pub had to rebuild it. I bruise it and paint it with neat industrial strength glysophate as it appears (both sides of the wall) and now there's hardly any. A different story along the road on the verge and in the council plant nursery, it's a veritable thicket in the summer. The council are not interested in eradicating it at all. Probably to do with costs. ::)
(http://i274.photobucket.com/albums/jj257/studyoulike/roundup.jpg)
the best weed killer out there ;D