On April 17, 2017, about 1145 central daylight time, a Grumman Schweizer G-164A airplane, N9533, sustained substantial damage during a forced landing after a loss of engine power in the vicinity of Palmer, Kansas. The commercial pilot was not injured. The airplane was registered to Hunninghake Aerial Spraying LLC, Baileyville, Kansas, and the aerial application flight was being conducted under the provisions of Title 14 Code of Federal Regulations Part 137. Visual meteorological conditions prevailed throughout the area and a flight plan was not filed. The flight originated at 1030 from the pilot's private airstrip near Baileyville, Kansas. According to the pilot, the aircraft was flying in a southerly direction over the application area when he heard a "pop" sound. The pilot then heard a louder "pop" sound, and the engine lost power. The pilot continued flying in a southerly direction about 1/3 of a mile before being forced to land. The pilot turned to the left to avoid a pasture fence and landed in a southeast direction in a newly planted wheat field. During the landing, the aircraft rolled over 5 terraces. Skid marks and numerous blade ground strikes where found at each terrace location. Ground scaring indicated that the propeller/engine separated from the aircraft before it spun 180° and came to a stop. The pilot exited the airplane uninjured. The right lower wing at the forward inboard spar and the engine firewall was found severely wrinkled. During the landing sequence, the hopper tank dump valve was opened and the herbicide chemical escaped. Examination of the engine at the accident site revealed a crack on an engine cylinder located at the 3 o'clock position of the Pratt & Whitney 1340 radial engine. According to log book entries, airworthiness directive AD 99-00-02 visual inspection for cylinder cracks, was completed at the last annual inspection conducted on November 28, 2016, about 37.1 hours prior to the accident.