The pilot reported that the agricultural airplane was loaded and was taking off when the accident occurred. He stated that he set the engine mixture control for best power and proceeded to take off. He stated that the takeoff roll took longer than expected and when the airplane was approaching the departure end of the runway he realized that the engine was not producing the power that he expected. As the end of the runway approached he added a second notch of flaps and the airplane lifted off and cleared the road and the corn crop on the opposite side of the road. The airplane's airspeed started to reduce and the pilot attempted to dump the chemical load, but inadvertently grabbed the flap handle and retracted the flaps. By the time he realized that he had inadvertently retracted the flaps the airplane impacted the corn crop and terrain and subsequently came to rest inverted. The airplane suffered substantial damage to the wings and fuselage. The pilot surmised that he had inadvertently leaned the engine mixture control too much prior to the takeoff which resulted in a reduction in available engine power. He made no mention of any pre-impact deficiencies with regard to the airplane.