On July 6, 1999, at 0722 central daylight time, a Grumman G-164B agricultural airplane, N6703Q, was substantially damaged upon collision with crops and terrain while maneuvering near Iowa, Louisiana. The non-instrument rated commercial pilot, sole occupant of the airplane, sustained minor injuries. The airplane was owned and operated by O'Brien Flying Service of Iowa, Louisiana. Visual meteorological conditions prevailed for the 14 Code of Federal Regulations Part 137 aerial application flight for which a flight plan was not filed. The airplane departed from the operator's airstrip, approximately 10 minutes prior to the accident. The operator reported that the biplane was dispatched with a load of 225 gallons of fungicide to spray a flooded rice field located about 3 miles west of his airstrip. While performing a spray pass on an easterly heading, at an airspeed of 100 mph, the airplane's main landing gear came in contact with the rice field. The operator added that "the wheels bogged down in the field," and the airplane nosed over coming to rest in the inverted position. The operator stated that the field being sprayed was bordered on the south by a highway that, due to a construction detour, was heavily traveled by trucks. The wind on the morning of the accident was from the northeast. He added that the pilot was trying to avoid over spraying the vehicles on the highway, and his attention was momentarily diverted from keeping his clearance from the field being sprayed. The application passes are normally performed at 6 to 7 feet above the crops. The 1,450-hour pilot, who had accumulated 925 flight hours in the accident airplane, did not report any mechanical problems or anomalies prior to the accident. In the enclosed NTSB Form 6120.1/2, the pilot reported that he had flown 277 hours in the preceding 90 days, with 141 hours within the last 30 days. Examination of the wreckage by the operator revealed that all four wings and the empennage sustained structural damage.