Daniel Jones

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Talkback: Japanese knotweed

Posted: 17/12/2012 at 22:35

Hi Alan,

Apologies if my posts are bit blunt - some of the methods to remove knotweed just wont work and they are expensive, plus they have a range of further negative impacts upon the environment... Ill leave ranting anymore about it after this post!

Will address your post and add some further info. Before I start, I agree with you! 

“Hi some time ago we were thinking of purchasing a house in Pembrokeshire and in the suryey notweed was found on the land,let me just say that after talking to the surveyer ,the council ,the solicitor i was amazed at the effect Jap Knot can have on the garden AND the surrounding areas,i was warned that it would be my job to get rid of it and if it could be proved  that it had spread to anyone elses property i would be to blame and suffer the cost of removal,”

This is very true, to an extent. The law states that you “should not allow Japanese knotweed (JK) to grow in the wild”. What actually constitutes the wild is a difficult point in itself: proving you did spread JK , following purchasing an already infested property is even harder. However, surveyors at present are jumpy (in some cases reasonably so, quite often, not so much!); I saw a guy declined for a mortgage with one stem of JK in his garden and a huge stand at least 5 doors down (more than 75m away). This might sound reasonable, until you realise he was in South Wales: there are quite a lot of places with a little bit of JK and loads just around the corner! This is not a reasonable approach to dealing with JK.

Further, in terms of control, particularly with respect to excavating JK rhizome; even herbicide treated “dead” JK rhizome - please dont do it. It is exceptionally difficult to tell whether it is alive or dead. Incidentally revised figures for JK rhizome regeneration rates suggest that as little as 0.068g (rather than 0.7g) will produce a new plant. Its hard to tell if its all dead - there could be kilos of it... also remember that stems and leaves will produce a new plant - this is not a scare story, there is scientific literature relating to it (please see Google Scholar). Throwing it in domestic waste, even if it looks dead is very risky and could be interpreted as “deliberate” introduction to somewhere else - “wild” (even if its a landfill site!).

“my solicitor gave me a phone number of a specialist in Jap Knot who i spoke to,he explained all the do,s and donts about this plant and how to get rid of it,most people who try the job themselves fail, becouse of other problems as well we decided not to buy,i have the phone number of this specialist if anyone wants to talk to him ,he is a very nice chap and knows exactly what he,s talking about ,if i came across Jap Knot again i would not even try to get rid myself i,d call this man for advise, if anyone wants this phone no Email me and ill send it to you , please dont think im scare mongering ,im not as this weed has caused many a tear  for many people”

Absolutely, if you are not confident in herbicide application and dont have the time/inclination to follow it up, dont try ad-hoc interventions etc. If you are based in Pembroke, Im sure this specialist is a good deal. In other circumstances, get at least a few quotes - most companies (particularly smaller ones) will charge a lot, for a short-term service. What you should look at is not only the herbicide type etc., but the number of visits “billed” by the company. Companies that undertake to revisit your property for a number of years within your contract (what youre paying for) are effectively acknowledging that repeat site visits will be required. 

However, if you are to going to attempt control, here are some good (and not so good!)

Talkback: Japanese knotweed

Posted: 17/12/2012 at 22:31

@galesrus - sounds like a nightmare and completely agree with your statement RE introducing new species to an area...

Found this online - by the looks of it, Gunnera is definitely another triffid (see page 5 onwards!). 


Talkback: Japanese knotweed

Posted: 13/12/2012 at 10:55

Additionally, dont use diesel or salt to control knotweed - neither is effective and diesel (in particular) is toxic to plants and animals. Just a point, but treating a large patch of knotweed with salt would be very expensive...!

Talkback: Japanese knotweed

Posted: 13/12/2012 at 10:51

Hi Folks, 

Just to clarify:

"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."

This is not legal - all material should be disposed of in licenced landfill. This is for two prinicipal reasons: 1) rhizome may remain viable for decades and 2) herbicides may induce dormancy, not kill. If you are satisfied that your herbicide treatment has worked, leave the knotweed alone (disturbance is likley to promote regrowth), or as another poster suggested, burn to ash in situ, following excavation.

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