[Jedd]

I had to look up black grass, as we don't have that particular weed in AU. I don't have any answers, of course, but a search on 'permaculture response in europe to black grass' gives some fairly unsurprising responses.

Broadscale monoculture invites its own range of problems, and herbicide-resistant highly-competitive (when in a single-other-species ecosystem) weeds are one such.

If the starting position is 'we must grow the same variety of wheat in the same field every year', then indeed, you're going to have some challenges.