On March 10, 1999, about 1055 hours Pacific standard time, a Bell 206B, N901CA, operated by Bettencourt Flying Service, Inc., collided with trees near Delhi, California, while performing an aerial application flight under 14 CFR Part 137. The helicopter was substantially damaged, and the commercial pilot received a minor injury. Visual meteorological conditions prevailed. The local area flight originated from Delhi about 1030. The pilot reported that seconds prior to the mishap, no cockpit annunciator lights were illuminating, no unusual vibrations were felt, fuel was in the tank, and the engine power was about 100 percent. The pilot said that after spraying a field, he was returning to the helispot to reload when he flew past 30-foot-tall almond trees and 10-foot-tall oleander bushes at a low altitude. Immediately thereafter the helicopter began yawing, the tail rotor felt sluggish, and control was lost. The helicopter came to rest on its right side. The pilot further reported that he believes the spray boom may have clipped the vegetation. At the time of the accident, the local wind condition was described by both the pilot and a ground witness as being light and variable. The pilot did not assert that any mechanical malfunctions precipitated the accident.