According to the operator, during a spray run of a cotton field, the airplane collided with an unmarked power line. The pilot then immediately landed in the cotton field. The operator also stated that the pilot was familiar with the field he was spraying and thought that the airplane was clear of power lines so he initiated a climb, resulting in the contact. Postaccident examination of the airplane revealed that approximately 1 foot of the vertical stabilizer and rudder assembly were separated. Additionally, arcing was noted on the right wing lift strut, and the propeller was damaged.