Land Plants - invasive

Knotweed (unknown species) (Fallopia sp.) on Jul 7, 2020

Submitter has sample
EDRR Status: Local expert notified

Description of specimen

I have tried to dig it up but the bright orange roots are so invasive I would need to excavate down 3-4 feet to eradicate them. I tried clipping the stem and shooting Roundup down the stem. It has made a small inpact on the plants in my upper area but the slope will be impossible to get to because it is steep. It is spreading quickly and I do not think my neighbor understands what is happening, nor am I sure they would care!. I thought I could dig them all up but it does not seem possible. Can we get some outside help on this? I will also contact the Clackamas County soil conservation district.
Thanks in advance for any help/suggestions you can provide.
This is down the slop showing the now 5' high forest that goes down to the creek. The dirt you see in the upper corner is the neighbors yard on the other side of the stream This shows where I have tried to dig up the roots at the top of the slope and down into the now forest of knotwood This is is a better shot of the mass.