Japanese Knotweed Management On Boarder of Property

I bought a property a year ago in NW Oregon and have been designing and creating my food forest on my 1/4 acre lot and did not put any thought into what was growing in the undeveloped lot boarding the entire backside of my property until the other day. I knew there was blackberry and am very familiar with having to cut it back from neighboring properties, but I noticed that there is also a massive thicket of Japanese knotweed fighting it out with the blackberry right up up against my fence and now I’m concerned about it aggressively growing under the fence and strangling everything I have planted along the fence. Looking for recommendations on how to be deal with this. I am not sure exactly who owns the lot of land or how to start trying to track that information down.