On August 22, 2001, about 0950 mountain daylight time, a Schweizer Aircraft G-164B, N3632T, registered to and operated by Ken Spray LLC, as a 14 CFR Part 137 aerial application flight, nosed over during the landing roll at Joslin Field - Magic Valley Regional airport, Twin Falls, Idaho. Visual meteorological conditions prevailed at the time and no flight plan was filed for the local flight. The aircraft was substantially damaged and the commercial pilot, the sole occupant, was not injured. The pilot reported that during the landing roll on runway 7, at approximately 35 to 40 mph, the aircraft developed a "substantial shake..." The tail then lifted and the aircraft nosed over and came to rest inverted. The pilot later reported that he did not apply the brakes nor did the tires slide. The aircraft was righted, and towed to the hanger. During the tow, the brakes were tested. No evidence of a mechanical failure or malfunction was found.