The commercial pilot was making his first spraying pass of the day when the agricultural airplane struck and damaged a center pivot irrigation system. The impact damaged the irrigation system, and the right main landing gear and tail wheel separated from the airplane. The airplane immediately started a descending bank to the right. The pilot reported that the right aileron was jammed in the full up position and control stick movements had no affect on the right aileron. He was able to use full power, full left aileron, and full left rudder to regain partial control and return to the airport for an emergency landing. As the airplane touched down the left main landing gear separated and the airplane came to rest upright with resulting substantial damage to the fuselage and flight controls. The pilot reported there were no mechanical anomalies prior to impact with the irrigation system. He also reported his forward vision was partially obscured by chemical spray on the windshield.