If you're cash crop is plant A, then plant B needs to be cheaper than spraying herbicides and the cash value of all the plant A you could have grown instead.

I believe this is called intercropping, although both plants A and B are meant to be harvested.

https://en.m.wikipedia.org/wiki/Intercropping

I definitely agree with your point, there may not be a need for a high tech solution to that problem.

I would be curious what ratio of producing vs protecting rows a farmer would need. Perhaps it’s less than alternating rows, not harming yield as drastically. Perhaps 1/4 or 1/5 would do.