On August 25, 2016, about 1250 central daylight time, a Piper PA-25-235 single-engine airplane, N4963Y, was substantially damaged during an off-airport forced landing near Bushton, Kansas. The pilot sustained serious injuries. The airplane was registered to a private individual and was operated by Wayne's Ag Aviation; Ellsworth, Kansas, as a Title 14 Code of Federal Regulations Part 137 agricultural application flight. Visual meteorological conditions prevailed, and no flight plan had been filed. The local flight departed Ellsworth Municipal Airport (9K7), Ellsworth, Kansas, about 1130. The pilot was applying pesticide to a field when there was a partial loss of power and the engine did not respond to throttle inputs. The pilot flew straight ahead, colliding with tall milo crops, and the airplane came to rest inverted. There was a post-impact fuel and pesticide leak, but no post-impact fire. There were no witnesses to the accident. Federal Aviation Administration (FAA) inspectors examined the engine on August 30, 2016. They reported finding no evidence of pre-impact catastrophic mechanical malfunction. Mechanical continuity was established during hand rotation of the crankshaft. The spark plugs electrodes remained mechanically undamaged and exhibited coloration consistent with normal operation. Spark was obtained from the magnetos. All fuel lines were found to be in place and secure. Fuel consistent with the appearance and odor of aviation fuel was noted. The gascolator and carburetor fuel screens were clean. The throttle/mixture controls were found securely attached at their control arms on the carburetor. and continuity to the cockpit was established. The air cleaner was free and clear of foreign objects. The engine had straight pipes and no muffler. According to the FAA "Carburetor Icing Prevention" chart, under the conditions that prevailed, serious icing was possible at glide power.