The commercial pilot was repositioning a single-engine agricultural airplane to a private grass strip when the engine lost power while on final approach. The pilot was unable to maintain his altitude so he made a forced landing to the only suitable field available. However, during the roll out he applied the brakes to avoid colliding with a large sprinkler apparatus and flipped over. As a result the vertical stabilizer and the rudder were substantially damage. Further examination of the radial engine by the operator revealed that the flexible intake hose had come loose and was ingested into the carburetor blocking the throat of the carburetor.