On Saturday, September 25, 1993, at 1730 eastern daylight time, N7386X, a Cessna 150B, owned and operated by John R. Haines of Nokesville, Virginia, overran the runway and collided with pine trees during landing at a private grass strip in Woodford, Virginia. Visual meteorological conditions prevailed and a flight plan was not filed. The certificated private pilot and his passenger were not injured. The airplane was substantially damaged. The personal flight originated in Woodford, Virginia, and was conducted under 14 CFR 91. The intended destination was Manassas, Virginia. According to the pilot, he obtained a weather briefing earlier that indicated favorable weather conditions for his route of flight. He stated that he departed and about five miles from Woodford, he noticed that the weather was deteriorating. He reversed direction and upon his return to the airport, it was raining heavily. He stated that he set up for a landing on runway 27, a grass strip which is 2600 feet long. He stated that he was high on final approach, but he thought he could make it. He also reported that he applied the brakes, but he was unable to stop on the wet grass strip. An FAA Inspector reported that the airplane touched down 2/3 down the runway and exited the runway for approximately 200 feet and collided with a stand of 5 foot high pine trees. The pilot reported that there was no mechanical malfunction and the accident could have been prevented if he had executed a go- around and set up for a short field landing.