Knotweed responds well to stem injection..Ive had area treated around my property to prevent invasion into my land.
A few "bonsai" type re growths have struggled through and these will be sprayed later this season..the area will then have watch n wait brief..
Post stem injection last year, once all had died off I cut and burnt all dead plants and whatever crowns I could get up.
This year most of area is dock weeds.
I would like to extend treatment area but this relies on co-operation from local farmers..one of whom seems to think all they have to do is scrape it all up and burn...if the root system is disturbed it will spread..if the root system of stem injected plants is disturbed it will relive..
Stem injection puts knotweed into dormant state and as long as its undisturbed it remains that way.
They are trialling a bug but its early days and also some electric zapping tool..that sounds interesting as it wouldn't then use strong chemicals.
The area I live is infested with both knotweed and himalayan balsam..there is a worrying attitude of ignore..in fact one of my neighbours claimed not to see any..
For mortgage purposes they want 21ft clearance around properties..however some lenders still refuse.
Once I knew I had a problem I just researched and treated...ignore and it'll spread.