On May 28, 1995, about 1810 mountain daylight time, N31580, an Air Tractor AT-301A airplane, operated by Desert Air Ag, Terreton, Idaho, collided with terrain while maneuvering during an aerial application and was substantially damaged in Terreton. The commercial pilot, the sole occupant, received minor injuries. Visual meteorological conditions prevailed and no flight plan had been filed. The flight departed from Mud Lake, Idaho, and was conducted under 14 CFR 137. According to an FAA aviation safety inspector from Salt Lake City, Utah, witnesses in the area reported gusting winds and thunderstorms in the vicinity of the accident site at the time the airplane was maneuvering over a field to spray herbicide. The pilot stated that after making three passes on the field, he encountered a very strong downdraft from an approaching thunder cell. He attempted to correct the loss of altitude and airspeed by dumping the load and turning to lower terrain. He was not successful in these attempts and the airplane could not gain enough airspeed to keep from striking the ground. The airplane sustained substantial damage at impact with rocky terrain.