Re: weed herbicide resistance, two further observations.
First, Pam Smith's article on HPPD (e.g. Callisto) resistant waterhemp.
A waterhemp population in a central Illinois seed corn production field has been shown to withstand foliar applications of the popular herbicide. University of Illinois weed scientist Aaron Hager says the wily weed has already adapted to resist four other classes of herbicides (triazine, PPO inhibitors, glyphosate, ALS inhibitors) in the state, but HPPD-inhibitor resistance has never previously been recorded. [More]In fact, as I was mowing roadsides I think I may have been staring some of this stuff in the face.
Second - and purely anecdotal - the sprayer operator from my fertilizer/chemical dealer called to check what I had planted in an adjacent field as he was respraying a neighbor's beans because the ragweeds don't seem to be paying attention to the glyphosate. As we shot the breeze, this grizzled veteran of thousands of sprayed acres suggested the new weed to watch around here was velvetleaf. It seems the usual dose of glyphosate just speckled the leaves in many cases. Waterhemp and marestail were old news, of course.
As always, we all can place our own bets. I don't think this involves my widely suspected socialist tendencies, but FWIW, I'm proceeding as if everything I battle weed-wise is glyphosate resistant.