The pilot performed a pre-flight inspection and noted the 61-gallon fuel tank was just over a quarter full. After about 26 minutes of aerial application runs, the helicopter yawed left and a warning light flickered. The pilot did not see which light had illuminated. Thinking it was a fuel problem, he checked the fuel quantity gauge, which read two needle-widths below a quarter tank. The pilot continued spraying and several seconds later the turbine-engine stopped producing power. The pilot turned left and made an autorotation run-on landing to a field. After the helicopter came to a stop, the main rotor blades flexed downward and severed the tail boom. Approximately 1.75 gallons of fuel was drained from the two fuel tanks. The pilot reported the usual fuel consumption was about 25 gallons per hour and the tanks had about 4 gallons of unusable fuel. The pilot said there were no mechanical problems prior to the accident and the engine was most likely starved of fuel due to the low fuel level and unusual attitudes inherent to helicopter aerial applications.