That one in the picture is definitely a male and is actively producing pollen. If you don't want seeds you need to kill that thing in a hurry. Put a trash bag over it before you cut it off or pull it out. You definitely have some female plants there as well, so you already have some pollination happening. They are wind pollinated and if they're within a hundred yards they've probably started catching pollen. Kill the males now and you'll be okay.

I had one plant this year it didn't show its sex until it was over 8 1/2 ft tall...