If you still want to try to save the beans, I, myself would try Basagran: http://www.cdms.net/LDat/ld89N004.pdf

I have smoked horseweed that is up to 4-6' high.....although that was in the fence line and I was using my spot sprayer.

You will have to soak them to get good coverage. Lots of water. And make sure you have the crop oil & AMS in the mix to heat it up. This will cause quite a bit of leaf burn in the beans too, but at this point your main goal is to keep those buggers from going to seed, and having some beans to harvest is a secondary goal.

Good luck.