The pilot reported that he had successfully flown five aerial application flights prior to the accident flight with loads that were only half of capacity. This make/model airplane was new to the pilot, but he felt comfortable with the airplane having accumulated about 15 hours at the time of the accident. During the takeoff roll, the airplane hit a bump about halfway down the runway, and started to porpoise. The pilot stated that he started losing directional control, and applied the brakes. After regaining control, the airplane was not aligned with the runway; however, he continued the takeoff, thinking that the airplane was going to fly. The airplane subsequently departed the runway surface, collided with a three-strand wire fence, and bounced across a dike. The collision with the fence damaged the landing gear, and the airplane skidded to a stop. Both wings, both main landing gear, and the engine mount sustained substantial damage. The pilot reported no mechanical malfunctions or failures with the airplane or engine that would have precluded normal operation.