The helicopter pilot reported that, during an agricultural application flight and while heading east about 3 ft above ground level, the "wind suddenly shifted, a gust of wind [came] from the west," and the helicopter "settled." The pilot increased power and raised the collective, but the helicopter impacted terrain. The helicopter sustained substantial damage to the fuselage and tailboom. The pilot reported that there were no preaccident mechanical malfunctions or failures with the helicopter that would have precluded normal operation. The pilot further reported that the helicopter was equipped with a muffler, which he believed adversely affected the engine's performance. However, correspondence with the helicopter's certificate holder stated that there would "be no reduction of horsepower with the muffler installed if done as per the instructions per the STC [supplemental type certificate]." An automated weather observation station located 5 nautical miles east of the accident site reported that, about 8 minutes before the accident, the wind was from 180° at 16 knots, gusting to 25 knots and that, about 32 minutes after the accident, the wind was from 180° at 16 knots, gusting to 26 knots.