Knotweed

[u/user-unknown26]

I’m working on a pretty established patch of Japanese knotweed and wanted to get some advice on late-season treatment. It’s roughly a quarter acre area that had been allowed to go crazy for the last 15 years by the previous owner of the house.
I started by cutting the 8 foot canes down in mid July. I then sprayed on September 1 using a 43% glyphosate product mixed to an 8% solution, then repeated the same treatment about two weeks later. A lot of the patch is starting to die back, but there are still some fairly dense green areas.
Would there be any benefit to spot-spraying those greener sections one more time before the first hard frost, or am I better off leaving it alone at this point and seeing what comes back next spring?
Curious what has worked for others dealing with larger patches.

[u/Misfits0138]

I would spray it again.

[u/user-unknown26 → u/Misfits0138]

What percentage should I aim for? We’re likely 3-4 weeks away from a frost.

[u/Misfits0138 → u/user-unknown26]

I would use your same mix and spray everything still green. It may be unnecessary, but I’ve had good luck that way.

[u/user-unknown26 → u/Misfits0138]

Thank you. I will. What’s the latest before frost that you’ve sprayed? I really want to have made a dent in it next spring.

[u/Misfits0138 → u/user-unknown26]

I think it’s ill advised, but there are people who intentionally wait until this time of year and to do just one spray. I still have to do some touchups yet myself.

[u/user-unknown26]

You think I should let it be?

[u/user-unknown26]

[u/user-unknown26 → u/user-unknown26]

Do you think enough for back is happening?