The pilot reported that during the agricultural operation he landed the helicopter into the wind to reload with fuel and agricultural chemicals. While the loader was mixing the chemicals, the pilot noted that the wind shifted to a tailwind condition. The pilot also noted that the rotor blades were dirty, but he forgot to clean them before departure. During the takeoff, the helicopter was unable to gain any lift and it started to sink back to the ground. The helicopter impacted the ground moments after takeoff with a slight nose low attitude which resulted in the skids collapsing and the main rotor blades contacting the tailboom. The pilot reported no preimpact mechanical malfunctions or failures with the airframe or the engine that would have precluded normal operation.