During a telephone interview, the pilot stated that he had been spraying a 300-acre field and had already made about 10 passes with the helicopter. He stated that after each pass he landed near a support vehicle to replenish the hopper. On the final approach to the support vehicle, the pilot did not see the wires and the helicopter struck them with the main rotor blades. The pilot landed the helicopter on an adjacent road without further incident. The helicopter sustained substantial damage to the main rotor blades. The pilot discovered that the driver of the support vehicle had moved the truck about 50 ft closer to the wires than it was previously positioned. He stated that the driver of the support vehicle did not inform him that the truck had been moved. The pilot stated that there were no mechanical problems with the helicopter before striking the wires.