AL-18 pilot reported experiencing intense vibration related to the loss of a propeller tip. Pilot landing safely in a field.

Narrative

Was flying along when a loud bang was heard and an intense vibrations. Engine RPM became unstable above 2000 RPM. Set the RPM below 2000 RPM and vibrations were present still just not was extreme. An attempt to troubleshoot was made. Oil pressure and Temperature remained in the normal operating range. I elected to land in a field rather than continue the flight. I attempted twice to make adjustments on the throttle in an attempt to make to a local private airstrip. Each addition of power made the vibrations worse. When coming over the trees for the field I killed the engine. At this time I still did not know the cause of the issue. Had the aircraft owner come out and look at it. It became apparent that the leading edge of the prop came off causing an imbalance on the prop leading to the intense vibrations. A new prop was put on and after a look over of the engine the aircraft owner said everything looked nominal. I flew it out of the field. I circled for a couple minutes and all indications were normal. Rest of the flight was uneventful.