PA-18 pilot reported during cruise the aircraft suddenly experienced a severe vibration. The pilot shut down the engine and glided to an open field and landed.

Narrative

While en route; I encountered deteriorating weather conditions and moderate turbulence in the vicinity of ZZZ. At approximately 2;900 feet MSL; the aircraft suddenly experienced severe vibration. My immediate assessment was that the propeller had suffered a mechanical failure. I elected to shut down the engine in order to prevent further damage and to maintain control of the aircraft.The surrounding terrain consisted largely of trees; with no suitable landing areas within 1-2 miles except for a small field; with uneven ground and half-moon ridges about 3 feet tall.Established best glide speed immediately after engine shutdown.Determined I would not reach the agricultural field under glide alone.Restarted the engine for approximately 10 seconds to extend my glide range; then secured it again.Executed a forced landing in the agricultural field. Due to prior backcountry flying experience; I was able to maintain control and land safely despite the short field length and uneven terrain.Post-incident inspection revealed that one of the nickel leading edge protectors on the Catto 86-inch; 2-blade propeller had separated in flight. The loss of this propeller component caused the extreme vibration that necessitated the emergency procedures. Aircraft was landed without further incident and no personal injuries were sustained. The field conditions resulted in a challenging but survivable landing.