The pilot was performing a straight in approach and landing. The airplane touched down on the runway centerline and under control. After the tailwheel settled onto the runway, the pilot applied the brakes and retarded the engine power into the beta range. Shortly afterward, the airplane began to swerve to the left. The pilot's efforts to maintain directional control were unsuccessful and the airplane departed the left side of the runway. The momentum of the airplane resulted in a "classic ground loop" as it encountered the soft ground adjacent to the runway and then contacted a crop of sugar cane. The airplane sustained damage to the fuselage, right wing and vertical stabilizer. The pilot noted that the "mishap was most likely preventable" because he did not ensure that the tailwheel lock was engaged before landing.