On July 10, 1996 at 1400 central daylight time (cdt), a Wsk Pzl Mielec M-18 Dromader, N2047S, was substantially damaged during a off airport landing at Waupaca, Wisconsin, following a partial loss of power. The airplane struck a ditch, during the forced landing, causing damage to the airplane's wing spars and skins. The commercial rated pilot was uninjured in the accident. The 14 CFR Part 137 aerial application flight was operating in visual meteorological conditions, and no flight plan had been filed. The flight originated from Bancroft, Wisconsin at approximately 1345 cdt. The pilot reported on NTSB form 6120.1/2 that he had just completed spraying a field of corn, when the engine lost power and went to idle. The pilot reported that the airplane's altitude was approximately 150 feet, at the time of the power loss. The pilot reported that he attempted to land the airplane in a hay field. The hay field turned out to be two hayfields, with a road running between them. Post flight examination of the airplane by a Federal Aviation Administration inspector revealed that the rod end on the throttle cable had separated from the cable. Examination of the rod end showed that the threads were stripped out. The rod end did have a hole drilled in it which allowed visual inspection for proper installation. The threads were not stripped out past the inspection hole, and a small piece of dirt approximately the same diameter as the inspection hole was found inside the rod end. The inspector reported that the jam nut on the rod end appeared to have been loose on the rod end. The inspector said the rod end was an Army-Navy (AN) part number. The total time on the rod end was listed at 2600 hours. The airplane's last annual had been completed on March 26, 1996, 120 hours before the accident. During a telephone discussion with the aircraft operator, he believed that the rod end used was not the correct thread type. The operator thought the rod end thread was a metric thread, and was not correct for the control cable being used. Advisory Directive (AD) number 90-20-04 reports that to prevent failure of the engine throttle cable, and the propeller governor cable both cables should be changed within the next 100 hours time in service. The operator of this aircraft reported that this AD had been complied with on this airplane.