On July 24, 2009, about 1445 Pacific daylight time, a Sikorsky S-55, N1255T, encountered rough terrain during an off airport emergency landing near Chelan, Washington. The pilot/owner was operating the helicopter under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The certificated commercial pilot was not injured; the helicopter sustained substantial damage to the fuselage from impact forces. The local other work flight departed Chelan about 1245. Visual meteorological conditions prevailed, and no flight plan had been filed. The pilot was drying cherries at low altitude when the helicopter lost hydraulic pressure. He flew the helicopter up to clear the trees, and made a run-on landing into a vacant field. The helicopter encountered a large hole that he had not seen, and the main rotor severed the tail boom. The operator reported that post accident examination revealed that an internal seal had leaked resulting in the loss of pressure in the hydraulic system. To date, the National Transportation Safety Board Pilot/Operator Accident Report Form 6120.1/2 has not been submitted.