On March 10, 1997, about 1700 hours Pacific standard time, a Grumman G-164B, N36265, operated by Growers Air Service of Woodland, California, was substantially damaged at Winters, California. The pilot was not injured. Visual meteorological conditions prevailed for the agricultural operation and no flight plan was filed. According to the pilot, the engine failed during level flight. The pilot force landed the aircraft in a field and nosed over. Postaccident examination of the engine revealed that the No. 1 engine cylinder sustained a catastrophic failure of the head assembly. The engine reportedly had 650 hours since major overhaul with an unknown amount of hours on the cylinder assembly since new. Examination revealed a fatigue type failure. The operator failed to respond to requests to file a Safety Board form 6120.1/2, Pilot/Operator Aircraft Accident Report.