The pilot reported that he was carrying out an inspection of the area to be treated when the engine made an unusual noise and began to vibrate. The pilot immediately turned the aircraft for a return to the departure airstrip and when power was reduced the engine began to run roughly. The engine then began to loose power and the pilot had to pump the throttle to keep the engine going. The pilot said he reached the end of the strip and on touchdown the right wheel struck soft ground. The right wingtip then struck the ground, and the aircraft nosed over. The pilot was suspended upside down by the seat harness and was drenched by organophosphate leaking from the hopper. The pilot could not open the door due to the cockpit roof being buried in mud. He was then forced to kick the window out to evacuate, and lost portion of his ring finger and broke bones in his left hand during his egress.
