The aircraft stalled into the ground after a dive and accelerated pull-up during aerial application. The pilot stated that he was doing the steep pull-ups and dives because of proximity to the city of Burlington, CO. He said the aircraft was just about empty of gas and chemical spray as he made the cleanup pass when the accident happened. He dove from about 300 ft at a 60-70 degree dive to within 50 ft of the ground before beginning to flare. He estimated the indicated airspeed at 105 knots when he started the flare. During the flare, the aircraft shuddered. He stated that during the pull-up wing over turn around maneuver the aircraft never shuddered and the stall warning did not sound. When the aircraft shuddered during the pull-out of the dive, the pilot said he released back pressure for a second and the aircraft impacted the ground in a 3 point attitude. The aircraft pancaked hard and slid 75 yards. The landing gear collapsed on impact. The ground elevation at the accident site is about 4178 ft. The density altitude was figured to be 7500 ft.