On May 9, 1999, approximately 1420 Pacific daylight time, the pilot of a Piper PA-18-150, N7483L, collided with tall brush while attempting a forced landing in a field about 1/2 mile short of the runway at McNary Field, Salem, Oregon. The private pilot was not injured, but the aircraft, which was owned and operated by the pilot, sustained substantial damage. The local 14 CFR Part 91 flight, which was being conducted in visual meteorological conditions, began about one hour and 30 minutes prior to the accident. No flight plan had been filed, and there was no report of an ELT activation. According to the pilot, as he was returning from the pleasure flight, he contacted Salem Tower and was cleared for a straight-in VFR approach to runway 34. While about five miles from the airport, he reduced the engine power to a setting less than it had been at during cruise flight, and started a descent from about 2,000 feet above the ground (AGL). About half way through the descent, the pilot pulled the throttle to idle but did not apply carburetor heat. When he was about 400 feet AGL, the pilot realized he was getting low on the approach, so he moved the throttle forward, but there was no response from the engine. He applied carburetor heat, but was unable to get the aircraft to restart. He therefore made a forced landing in a field about 1/2 mile from the end of runway. During the landing roll, the pilot maneuvered to miss a fence post he had not seen from the air, but in so doing, the aircraft collided with tall shrubs and sustained substantial damage. Subsequent to the accident, the aircraft was moved to McNary Field where the engine was test run and inspected. The inspection revealed no anomalies, and during the test run, the engine operated normally with proper responses to magneto and carburetor heat checks. The investigation revealed that the surface weather observation (METAR) taken at Salem Airport at the time of the accident (2120 UTC) showed a temperature of 54 degrees Fahrenheit and a dew point of 36 degrees. According to the Carburetor Icing Probability Chart obtained from DOT/FAA/CT-82/44 (see attached chart), the pilot was making the approach in conditions where serious carburetor icing could be expected at glide power. A review of the PA-18 Owners Handbook revealed that, although carburetor heat is not required for all approaches and landings, it is required when "...icing conditions prevail."