At $6.28 per gallon and rising, fuel costs are hammering farmers and truckers this fall.

For Erik Oberbroeckling, a corn and soybean farmer near Garnavillo who also owns a mixed-fleet trucking business, skyrocketing diesel prices mean that fuel has officially surpassed labor as the single highest operating cost for running a semi.

“Fuel and labor used to be kind of neck and neck, but once diesel went where it did, now fuel has surpassed...