On March 18, 1996, about 0800 Pacific standard time, N57362, a Bell 206B helicopter, operated by Pioneer Aviation, Inc., La Grande, Oregon, impacted trees and terrain and was substantially damaged while maneuvering near La Grande. The commercial pilot, the sole occupant, received minor injuries. Visual meteorological conditions prevailed and no flight plan had been filed. The aerial application flight was conducted under 14 CFR 137. The pilot reported that after performing a low-altitude aerial application spray run, he initiated a climb to clear trees. The left spray boom impacted one of the trees and the helicopter began to rotate to the right. The pilot applied full left pedal, but the helicopter continued to rotate to the right. The pilot further stated: My main objective was to continue to maintain control of the helicopter in order to avoid injury to the surrounding residents or damage to structures. I reduced the pitch on the main blade with the collective to slow rotation of the helicopter just enough to stay clear of the trees. Using the cyclic and collective I milked my way toward the middle of the field, southwest of the trees. I continued to work the pedals with no response. The helicopter continued to rotate while descending to land. The ship maintained a level attitude throughout the decent until the skids impacted the ground. After hitting the ground, the helicopter sprung up and rolled over, coming to rest on the left side. According to an FAA aviation safety inspector from Boise, Idaho, the cabin and tail boom were substantially damaged. No preimpact mechanical malfunctions were reported.