On June 18, 2009, about 0600 Pacific daylight time, a Grumman G-164A, N9723, impacted the ground while maneuvering to spray a field about 3 miles east of the Yerington Municipal Airport (O43), Yerington, Nevada. Ag Air, Inc., operated the airplane under the provisions of 14 Code of Federal Regulations Part 137, as an aerial application flight. The airplane was structurally damaged. The pilot, the sole occupant, received minor injuries. Visual meteorological conditions prevailed for the local area flight, and no flight plan had been filed. According to the pilot, he had finished spraying a section of an onion field. He made a 180-degree turn back to re-enter the onion field to spray another swath. After completing the turn and rolling wings levels, he stated that he experienced a loss of aileron control, which resulted in the airplane settling toward the ground. He reported that the airplane still had pitch control, so he attempted to lower the nose to maintain airspeed until he was able to regain aileron control. Prior to ground contact, he made an attempt to flare to cushion the impact. After the airplane landed hard, it came to a sudden stop and came to rest upside down. The operator reported that the pilot started spraying an organic insecticide on the onion field about 0530. He reported the weather conditions as 10 miles plus visibility; clear skies; no wind; and a temperature of 58 degrees Fahrenheit. A Federal Aviation Administration inspector responded to the site and was able to establish flight control continuity of the airplane, and mechanical continuity of the engine.