You can burn it in the car, but you'll probably get code 0174- lean mix fuel trim. I hit that when I was experimenting, at around 40% ETOH in the HAH.

Deere will tell you NOT to use E85. All engines are ok for E10, though. And in reality, E85 should work in the tractor, but you may have to keep it choked or drill out the carb jets. And Deere won't fix it. Its all a matter of how comfortable you are doing your own maintenance and repairs.