The pilot had just begun crop dusting when a gust of wind forced him into the ground from a height of approximately one hundred and fifty feet. The airplane struck the ground in a left wing low and nose down attitude. The left side of the aircraft impacted a tree, resulting in substantial damage. The pilot said he was aware of a nearby thunderstorm but did not believe it would affect his flight. Upon exiting the aircraft the pilot estimated the wind to be approximately thirty miles per hour. It began to rain twenty minutes after the accident. No preflight briefing was received. The pilot reported no mechanical anomalies prior to the accident.