The pilot was conducting an aerial application flight at the time of the accident. Before spraying, he circled the field and noted high tension power lines. He completed 3 spray runs without incident, passing under the power lines on 2 of those passes. However, on the 4th pass, the pilot "did not maintain a low enough altitude" and the vertical stabilizer struck the lines. The upper portion of the vertical stabilizer and the entire rudder separated from the airframe. He was able to maintain control with a "total loss of rudder control" and executed a forced landing to a harvested wheat field.