On January 9, 1995, at 1740 mountain standard time, a Kaman HH- 43F helicopter, N321WN, collided with a tree and crashed into a field during a Part 137 aerial application flight near Glendale, Arizona. Visual meteorological conditions existed at the time. The aircraft was substantially damaged and the pilot was not injured. The aircraft departed from a private helicopter pad near Tolleson, Arizona, at 1730. According to the pilot, he had completed spraying the field and was cleaning up the ends. On the last pass, he did not see the bare tree branches that protruded 15 to 20 feet into the field until it was too late. He stated that the right main rotor blade struck the branches which tore off the control flap to the rotor blade causing a severe vibration. The pilot immediately landed in a muddy field and shut down the engine. Examination of the helicopter by the pilot revealed that the tail booms were cracked and broken by the severe vibrations. There was no fire, fuel, or chemical spill.