The Environment Agency can be seen here treating their worst-case scenario for Japanese Knotweed.
Our recommendation for treating Japanese Knotweed most effectively using Touch Pro is on new growth when the weeds are smallest and chemicals cannot be used. If the infestation is well established and there is a large crown, we recommend an integrated approach where the area is initially treated using chemicals or by pulling and then Touch Pro is used for new growth until the infestation has gone.
Having said that, the results on treating worst-case scenario Japanese Knotweed without any pre-treatment other than cutting it back look very positive as you can see from the photos where the treated area is in the middle of the photos with all of the regrowth from untreated areas surrounding it.
If you would like to know more, please do call.