The pilot reported that prior to the accident flight, there was a trainee pilot in the agricultural application helicopter, who preferred no friction on the controls. Once the trainee left, the pilot forgot to adjust the control friction. During the accident flight, the helicopter was spraying a wheat field at 55 mph, about 10 feet above the ground. The pilot let go of the collective to adjust the helicopter's "Crophawk" computer. The collective subsequently lowered and the helicopter impacted terrain. The pilot added that there were no preimact mechanical malfunctions with the helicopter. Examination of the wreckage by a Federal Aviation Administration inspector revealed that during the impact, the tailboom separated and the helicopter came to rest on its right side.