On April 4, 1998, at 1200 central standard time, a Grumman G- 164A, N48FS, operated by a commercial pilot, was destroyed by fire as the pilot was starting the engine. The accident occurred at a private airstrip in Benton, Missouri. The pilot was not injured. The aerial application flight was operating under 14 CFR Part 137. Visual meteorological conditions prevailed and no flight plan was filed. The pilot reported that he started the airplane and moved it out onto the airstrip where it was to be loaded with fertilizer. The engine was then shut down. It took approximately two hours for the proper loading truck to arrive and for the fertilizer to be loaded. The pilot stated he then returned to the airplane and attempted to start the engine at which time it backfired and quit. He reported he waited 15 to 20 seconds during which time he did not see any smoke so, he pumped the throttle three times and attempted to start the engine again. He reported that smoke instantly started coming out of the exhaust stack at which time the ground loader got a fire extinguisher and fired it into the exhaust stack. The pilot stated he pulled the mixture back, opened the throttle and continued to crank the engine for three or four minutes hoping to suck the flames into the engine. He reported that after this time he was forced to leave the airplane due to the heavy smoke. The pilot reported the winds were out of the north blowing the flames upward toward the top fuel tank which ignited. He reported that by time the fire department arrived the airplane was completed destroyed.