On September 6, 2013, about 0925 central daylight time, a Continental Copters Inc., OH13-H Tomcat agricultural helicopter, N9005T, registered to Scotts Helicopter Service Inc., of LeSueur, Minnesota, sustained substantial damage after it collided with the ground while maneuvering during an aerial application flight. The pilot was not injured. Visual meteorological conditions prevailed in the vicinity and no flight plan was filed. The aerial application flight was being conducted under the provisions of 14 Code of Federal Regulations Part 137. The flight originated from a private location near Gaylord, Minnesota, about 0920. The pilot reported to work on the morning of the accident for a scheduled day of flying after he had the previous day off. His first aerial application flight of the morning was uneventful and the helicopter landed to reload pesticides. The pilot then took off and successfully applied about 75 gallons pesticides to a field and proceeded to the next field located about 3 miles away at 300-400 feet AGL. While enroute the pilot wanted to call his truck driver over the two way radio. The radio connection to his helmet was unplugged, so he reached and plugged it in with his right hand while his left hand transferred from the collective to the cyclic. The pilot estimated that this process took about 5 to 8 seconds. Immediately after he plugged in the radio connection to his helmet, the collective slammed into a full down position and the pilot recalled seeing his black-colored notebook fly around the cabin due to the sudden collective movement. The pilot then quickly grabbed the collective and raised it up. He noticed that the helicopter was losing altitude and the main rotor RPMs were decreasing, with the engine RPM and main rotor RPM needles split. He recalls twisting the throttle control back and forth with no effect and attempted to autorotate. The helicopter touched down hard, sustaining substantial damage to the tailboom. An on site inspection of the accident site and the helicopter was conducted by an FAA inspector. The inspector reported that no mechanical or environmental anomalies were found that could have contributed to the accident. The pilot stated in the recommendation section of NTSB Form 6120, that could have chose to not unplug his helmet and keep his hand on the collective control at all times, which would have prevented the collective from slamming down while he was connecting his radio cables to his helmet. A review of the maintenance log books for the helicopter did not show any entries regarding malfunctions with the collective control during previous flights and the helicopter was operating normally during the first flight of the day. Additionally, this model helicopter does not have a friction control mechanism on the collective control, and if it is not held in place by the pilot, it could move up or down during flight.