The pilot reported he departed in the airplane with about 660 lbs of fuel and about 3,500 lbs of liquid chemical for application to a pasture. After arriving at the pasture, the chemical dispersal system was malfunctioning, and the pilot decided to return to the airport. During the landing to the first quarter of the runway, the airplane was about 125 mph, with “half flap” applied, and the tailwheel was locked. As the tailwheel touched down on the dry concrete runway, the pilot initiated beta mode with the propeller, and the airplane “started veering to the right.” The pilot assessed that he “reversed the propeller too aggressively and too soon.” The airplane departed the runway to the right, the left main landing gear separated after impacting a ditch, and the airplane came to rest upright on a grass field. The pilot was able to egress from the airplane without further incident. The airplane sustained substantial damage to the fuselage and the left wing. The operator reported there were no preimpact mechanical malfunctions or failures with the airframe or the engine that would have precluded normal operation. A postaccident examination of the chemical dispersal system found foreign object debris that was likely blocking the flow of the chemical. Title 14 Code of Federal Regulations Part 137 Agricultural Aircraft Operations does not contain full load landing training and recurrency requirements. The pilot reported the last time he performed a full load landing was about 2 years prior. The estimated density altitude for the airport was 6,101 ft.