On March 29, 2016, about 1730 central daylight time, an Air Tractor Inc AT-402, N4555E, stuck a wire/power line and impacted terrain during an aerial application of a field near Beyersville, Texas. The airplane sustained substantial damage. The pilot received serious injuries. The airplane was operated by Ranspot Flying Service under 14 Code of Federal Regulations Part 137 as an aerial application flight that was not operating on a flight plan. The local flight originated from the operator's private airstrip near Burlington, Texas about 1600. The pilot stated that the accident flight was the second and last aerial application for the day. The pilot circled the last field to be sprayed four times looking for obstructions and saw powerline poles on the east and west sides of the field, but he did not see an older unmarked powerline pole in the middle of the field. He said that it was gray and hazy day which contributed to making the older powerline pole difficult to see. The pilot sprayed the field in a north/south direction and during the fourth spray pass, the airplane struck the older powerline pole with the right wing, began a right spiral descent, and impacted the ground in a level attitude. The pilot applied full left rudder in an attempt to stop the spin and impact the ground in a level attitude. The pilot felt that with the haze and unfamiliarity of the field, another one or two circles of the field could have possibly led to his identifying the older powerline pole.