On June 18, 2014, about 1330 central daylight time, a Grumman G-164B airplane, collided with terrain during a forced landing following a partial loss of engine power during takeoff. The commercial pilot was not injured and the airplane was substantially damaged. The airplane was registered to and operated by McCormack's Crop Care by Air Inc. under the provisions of 14 Code of the Federal Regulations Part 137 as an aerial application flight. Visual meteorological conditions prevailed for the flight which operated without a flight plan. The local flight was departing a private airstrip at the time of the accident.According to a statement provided by the operator, the airplane was departing the private strip when the engine would not produce more than 90% power. The pilot was unable to get the airplane to continue a climb so he performed a forced landing to a road. During the landing roll, the airplane slid to the side of the road and impacted a ditch resulting in substantial damage to the fuselage. The airplane was recovered and sent for repairs with the agreement that the investigator in charge would be made aware of the maintenance results. The engine was removed from the airplane and sent to an unknown vendor for repair. The operator of the airplane has gone out of business and the disposition and location of the engine could not be determined. Honeywell could not find any recent maintenance activity reported on the accident engine. The reason for the partial loss of engine power could not be determined.