On May 1, 1999, about 1715 eastern daylight time, a Cessna 150J, N50943, collided with trees during climbout from a private airstrip near Seneca, South Carolina. The flight was operated by the private pilot under the provisions of Title 14 CFR Part 91 with no flight plan filed. Visual meteorological conditions prevailed at the time of the accident. The private pilot and passenger received minor injuries and the airplane was substantially damaged. The flight departed Pickens County Airport in Pickens, South Carolina, at 1700, enroute to Clemson, South Carolina. After refueling at Pickens, the pilot and his son flew to a friend's private airstrip near, Seneca, South Carolina. After takeoff, the pilot flew directly to his friend's airstrip. Upon arriving at his friend's airstrip, they noticed that his friend's car was not there, so the pilot's son suggested they make a touch and go landing before returning home. The pilot established a final approach for a normal landing with 40 degrees of wing flaps. After the touch down the pilot stated that he retracted the flaps, but noticed during the initial climb that the flaps had only retracted to 30 degrees. As he continued the climb the pilot retracted the flaps another ten degrees. Shortly after retracting the flaps to 20 degrees the airplane lost lift and altitude, and collided with trees on the departure end of the runway. No mechanical problems with the airplane were reported by the pilot. According to the Cessna 150 pilot's handbook, "flap deflections of 30 and 40 degrees are not recommended at any time for takeoff". Ten degrees of flap may be used for short or soft field takeoffs. The pilot stated that " in the future, wherever possible, I intend to stay off grass runways"; the departure runway was grass.