The pilot attempted to take off in the tailwheel-equipped agricultural airplane with a full load of chemical and a full load of fuel. During the takeoff roll the airplane swerved to the left and the pilot was unable to arrest the swerve. The airplane exited off the left side of the runway and impacted a taxiway sign, followed by the collapse of the left main landing gear. The airplane came to rest in an upright position alongside the runway and the pilot was able to exit unassisted. Following the accident the airplane was examined and a loose left landing gear attachment bolt was found, allowing the left wheel to pivot out of alignment during the takeoff roll.