If my memory is accurate, I was standing in a field of hemp in or around 2000/2001, just outside the west perimeter highway that surrounds Winnipeg, Manitoba. It was well over my head. The emphasis in that crop was on fibre production. (I can't remember the cultivar any longer) Just a few paces in and I had to turn back because of my allergies and the fact that the smell was so over powering that I couldn't hardly breath. The apparent humidity inside the standing crop was very noticeable compared to a slight breeze when standing outside it. (Probably very similar with corn)
I have some industrial sewing machines and would like to get hemp canvas for making a few bags that I currently make out of canvas; but have yet to find a good source.
As mentioned above, I imagine the weed control must be off the charts once the canopy is over a metre high... it was pretty shady the few feet that I ventured into that crop so long ago already.