On August 14, 2000, at 0730 central daylight time, an Air Tractor AT-502 agricultural airplane, N73184, was substantially damaged when it struck an irrigation sprinkler apparatus while maneuvering near Helena Arkansas. The airplane was owned and operated by the Riddell Flying Service, Inc., of West Helena, Arkansas. The commercial pilot, sole occupant, was not injured. Visual meteorological conditions prevailed, and a flight plan was not filed for the 14 Code of Federal Regulations Part 137 aerial application flight. The local boll weevil eradication flight originated from a staging strip south of Helena at 0700. According to the pilot, this was his first flight of the day, and he had completed spraying 35 acres of cotton. He was flying from east to west, and had crossed over some trees and dropped down for a swath run when the right wing struck an irrigation sprinkler pivot. About 5-6 feet of the right wing and half of its aileron separated from the airplane. The pilot flew the airplane back to the staging strip and landed without further incident. The pilot stated that the sun was in his eyes, and it hampered him from seeing the irrigation pivot in time to avoid it.