The pilot reported that the airplane encountered a downdraft after completing an aerial application pass. While climbing away from the field, the airplane’s right wing impacted a tree and the pilot performed an off-field landing instead of returning to the departure airport. The main landing gear collapsed during the landing in a rough field. A post-impact fire ensued on the right wing after the airplane came to rest. The airplane was substantially damaged. The pilot reported that there were no pre-impact mechanical malfunctions or failures that would have precluded normal operation of the airplane.