On March 19, 1999, at 1450 central standard time, a Schweizer, G-164B, N3629T, collided with trees during an emergency landing, following a loss of engine power in Bay Springs, Mississippi. The airplane was operated by Payne's Flying Service, Inc., under the provisions of Title 14 CFR Part 137, and visual flight rules. Visual meteorological conditions prevailed, and no flight plan was filed for the local aerial application flight. The pilot was not injured and the airplane sustained substantial damage. The flight departed from Bay Springs, Mississippi at 1440. According to the pilot, he was maneuvering at a low altitude, actively spraying chemicals on a stand of trees, when the engine lost power. The pilot selected an area for an off-airport forced landing. The airplane collided with trees during the attempted forced landing. The engine examination revealed an internal gearbox failure, and revealed metal debris, in the output housing at the forward scavenge strainer. There were also bearing remains recovered from the gearbox assembly. The examination of the fuel control drive train revealed that the intermediate gear had uncoupled from the dual idler gear and there was a bearing failure at the intermediate gear. The engine oil filter and chip detector were, removed and both were contaminated with metal particles. Approximately one hour of fuel was available in the fuel system during the wreckage examination. A visual examination of the remaining wing sumps failed to disclose visible water or contaminants.