On July 1, 1994, about 1600 central daylight time, a Callair A9B airplane, N2851F, operated by Pietsch Spraying Inc. of Minot, North Dakota, sustained substantial damage when it collided with terrain 12 miles southwest of Minot. The commercial pilot sustained no injuries. Visual meteorological conditions prevailed for the aerial application flight conducted under CFR 14 Part 137. The local flight originated at Minot International Airport about 1530. No flight plan was filed. The pilot reported the airplane was equipped with "super booms" which trail beneath the airplane. He said he was flying low to optimize spraying along the side of a hill. On the fourth pass he "went through a whirlwind and stuck the boom in the wheat." He said the airplane swung around, impacted the terrain, and stopped in approximately 300 feet.