On June 15, 2018, about 1010 mountain daylight time, a Grumman Aircraft Engineering Corporation-Schweizer G-164B airplane, N6672Q, impacted hilly terrain during an aerial application flight near Arrey, New Mexico. The commercial pilot sustained serious injuries. The airplane received substantial wing and fuselage damage during the impact. The airplane was registered to an individual and operated by Valley Ag Aerial Services as a Title 14 Code of Federal Regulations Part 137 aerial application flight. Day visual meteorological conditions prevailed in the accident area about the time of the accident, and the flight was not operated on a flight plan. The local flight originated from the Hatch Municipal Airport, near Hatch, New Mexico, about 0900.The operator reported that the pilot completed 4 aerial application loads "just fine." The pilot turned to do a clean-up pass of the field and crashed into a hillside. The pilot does not remember what happened nor why it happened. The operator reported that there were no mechanical malfunctions with the airplane. Another operator in the area had previously sprayed the accident field. He, in part, stated that there is rising terrain that borders the field on the East side. If it were to be sprayed in the morning flying East/West, the East facing swath would be into the sun and rapidly rising terrain. At 1010, the United States Navy Observatory reported the altitude and azimuth of the sun in Hatch, New Mexico, were 49.7° and 91.6° respectively. At 0955, the recorded weather at the Las Cruces International Airport, near Las Cruces, New Mexico, was: Wind 160° at 5 knots; visibility 10 statute miles; sky condition clear; temperature 31° C; dew point 7° C; altimeter 29.98 inches of mercury.